Linux Virtualization - Jul 2018 - [PATCH net-next v2 3/5] virtio_ring: add packed ring support

Hello everyone,

This patch set implements packed ring support in virtio driver.

Some functional tests have been done with Jason's
packed ring implementation in vhost:

https://lkml.org/lkml/2018/7/3/33

Both of ping and netperf worked as expected.

v1 -> v2:
- Use READ_ONCE() to read event off_wrap and flags together (Jason);
- Add comments related to ccw (Jason);

RFC (v6) -> v1:
- Avoid extra virtio_wmb() in virtqueue_enable_cb_delayed_packed()
  when event idx is off (Jason);
- Fix bufs calculation in virtqueue_enable_cb_delayed_packed() (Jason);
- Test the state of the desc at used_idx instead of last_used_idx
  in virtqueue_enable_cb_delayed_packed() (Jason);
- Save wrap counter (as part of queue state) in the return value
  of virtqueue_enable_cb_prepare_packed();
- Refine the packed ring definitions in uapi;
- Rebase on the net-next tree;

RFC v5 -> RFC v6:
- Avoid tracking addr/len/flags when DMA API isn't used (MST/Jason);
- Define wrap counter as bool (Jason);
- Use ALIGN() in vring_init_packed() (Jason);
- Avoid using pointer to track `next` in detach_buf_packed() (Jason);
- Add comments for barriers (Jason);
- Don't enable RING_PACKED on ccw for now (noticed by Jason);
- Refine the memory barrier in virtqueue_poll();
- Add a missing memory barrier in virtqueue_enable_cb_delayed_packed();
- Remove the hacks in virtqueue_enable_cb_prepare_packed();

RFC v4 -> RFC v5:
- Save DMA addr, etc in desc state (Jason);
- Track used wrap counter;

RFC v3 -> RFC v4:
- Make ID allocation support out-of-order (Jason);
- Various fixes for EVENT_IDX support;

RFC v2 -> RFC v3:
- Split into small patches (Jason);
- Add helper virtqueue_use_indirect() (Jason);
- Just set id for the last descriptor of a list (Jason);
- Calculate the prev in virtqueue_add_packed() (Jason);
- Fix/improve desc suppression code (Jason/MST);
- Refine the code layout for XXX_split/packed and wrappers (MST);
- Fix the comments and API in uapi (MST);
- Remove the BUG_ON() for indirect (Jason);
- Some other refinements and bug fixes;

RFC v1 -> RFC v2:
- Add indirect descriptor support - compile test only;
- Add event suppression supprt - compile test only;
- Move vring_packed_init() out of uapi (Jason, MST);
- Merge two loops into one in virtqueue_add_packed() (Jason);
- Split vring_unmap_one() for packed ring and split ring (Jason);
- Avoid using '%' operator (Jason);
- Rename free_head -> next_avail_idx (Jason);
- Add comments for virtio_wmb() in virtqueue_add_packed() (Jason);
- Some other refinements and bug fixes;

Thanks!

Tiwei Bie (5):
  virtio: add packed ring definitions
  virtio_ring: support creating packed ring
  virtio_ring: add packed ring support
  virtio_ring: add event idx support in packed ring
  virtio_ring: enable packed ring

 drivers/s390/virtio/virtio_ccw.c   |   14 +
 drivers/virtio/virtio_ring.c       | 1365 ++++++++++++++++++++++------
 include/linux/virtio_ring.h        |    8 +-
 include/uapi/linux/virtio_config.h |    3 +
 include/uapi/linux/virtio_ring.h   |   43 +
 5 files changed, 1157 insertions(+), 276 deletions(-)

-- 
2.18.0

Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
---
 include/uapi/linux/virtio_config.h |  3 +++
 include/uapi/linux/virtio_ring.h   | 43 ++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/include/uapi/linux/virtio_config.h
b/include/uapi/linux/virtio_config.h
index 449132c76b1c..1196e1c1d4f6 100644
--- a/include/uapi/linux/virtio_config.h
+++ b/include/uapi/linux/virtio_config.h
@@ -75,6 +75,9 @@
  */
 #define VIRTIO_F_IOMMU_PLATFORM		33
 
+/* This feature indicates support for the packed virtqueue layout. */
+#define VIRTIO_F_RING_PACKED		34
+
 /*
  * Does the device support Single Root I/O Virtualization?
  */
diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index 6d5d5faa989b..0254a2ba29cf 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h
@@ -44,6 +44,10 @@
 /* This means the buffer contains a list of buffer descriptors. */
 #define VRING_DESC_F_INDIRECT	4
 
+/* Mark a descriptor as available or used. */
+#define VRING_DESC_F_AVAIL	(1ul << 7)
+#define VRING_DESC_F_USED	(1ul << 15)
+
 /* The Host uses this in used->flags to advise the Guest: don't kick me
when
  * you add a buffer.  It's unreliable, so it's simply an optimization. 
Guest
  * will still kick if it's out of buffers. */
@@ -53,6 +57,17 @@
  * optimization.  */
 #define VRING_AVAIL_F_NO_INTERRUPT	1
 
+/* Enable events. */
+#define VRING_EVENT_F_ENABLE	0x0
+/* Disable events. */
+#define VRING_EVENT_F_DISABLE	0x1
+/*
+ * Enable events for a specific descriptor
+ * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
+ * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
+ */
+#define VRING_EVENT_F_DESC	0x2
+
 /* We support indirect buffer descriptors */
 #define VIRTIO_RING_F_INDIRECT_DESC	28
 
@@ -171,4 +186,32 @@ static inline int vring_need_event(__u16 event_idx, __u16
new_idx, __u16 old)
 	return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
 }
 
+struct vring_packed_desc_event {
+	/* Descriptor Ring Change Event Offset/Wrap Counter. */
+	__virtio16 off_wrap;
+	/* Descriptor Ring Change Event Flags. */
+	__virtio16 flags;
+};
+
+struct vring_packed_desc {
+	/* Buffer Address. */
+	__virtio64 addr;
+	/* Buffer Length. */
+	__virtio32 len;
+	/* Buffer ID. */
+	__virtio16 id;
+	/* The flags depending on descriptor type. */
+	__virtio16 flags;
+};
+
+struct vring_packed {
+	unsigned int num;
+
+	struct vring_packed_desc *desc;
+
+	struct vring_packed_desc_event *driver;
+
+	struct vring_packed_desc_event *device;
+};
+
 #endif /* _UAPI_LINUX_VIRTIO_RING_H */
-- 
2.18.0

This commit introduces the support for creating packed ring.
All split ring specific functions are added _split suffix.
Some necessary stubs for packed ring are also added.

Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
---
 drivers/virtio/virtio_ring.c | 801 +++++++++++++++++++++++------------
 include/linux/virtio_ring.h  |   8 +-
 2 files changed, 546 insertions(+), 263 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 814b395007b2..c4f8abc7445a 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -60,11 +60,15 @@ struct vring_desc_state {
 	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
 };
 
+struct vring_desc_state_packed {
+	int next;			/* The next desc state. */
+};
+
 struct vring_virtqueue {
 	struct virtqueue vq;
 
-	/* Actual memory layout for this queue */
-	struct vring vring;
+	/* Is this a packed ring? */
+	bool packed;
 
 	/* Can we use weak barriers? */
 	bool weak_barriers;
@@ -86,11 +90,39 @@ struct vring_virtqueue {
 	/* Last used index we've seen. */
 	u16 last_used_idx;
 
-	/* Last written value to avail->flags */
-	u16 avail_flags_shadow;
+	union {
+		/* Available for split ring */
+		struct {
+			/* Actual memory layout for this queue. */
+			struct vring vring;
 
-	/* Last written value to avail->idx in guest byte order */
-	u16 avail_idx_shadow;
+			/* Last written value to avail->flags */
+			u16 avail_flags_shadow;
+
+			/* Last written value to avail->idx in
+			 * guest byte order. */
+			u16 avail_idx_shadow;
+		};
+
+		/* Available for packed ring */
+		struct {
+			/* Actual memory layout for this queue. */
+			struct vring_packed vring_packed;
+
+			/* Driver ring wrap counter. */
+			bool avail_wrap_counter;
+
+			/* Device ring wrap counter. */
+			bool used_wrap_counter;
+
+			/* Index of the next avail descriptor. */
+			u16 next_avail_idx;
+
+			/* Last written value to driver->flags in
+			 * guest byte order. */
+			u16 event_flags_shadow;
+		};
+	};
 
 	/* How to notify other side. FIXME: commonalize hcalls! */
 	bool (*notify)(struct virtqueue *vq);
@@ -110,11 +142,24 @@ struct vring_virtqueue {
 #endif
 
 	/* Per-descriptor state. */
-	struct vring_desc_state desc_state[];
+	union {
+		struct vring_desc_state desc_state[1];
+		struct vring_desc_state_packed desc_state_packed[1];
+	};
 };
 
 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
 
+static inline bool virtqueue_use_indirect(struct virtqueue *_vq,
+					  unsigned int total_sg)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	/* If the host supports indirect descriptor tables, and we have multiple
+	 * buffers, then go indirect. FIXME: tune this threshold */
+	return (vq->indirect && total_sg > 1 &&
vq->vq.num_free);
+}
+
 /*
  * Modern virtio devices have feature bits to specify whether they need a
  * quirk and bypass the IOMMU. If not there, just use the DMA API.
@@ -200,8 +245,17 @@ static dma_addr_t vring_map_single(const struct
vring_virtqueue *vq,
 			      cpu_addr, size, direction);
 }
 
-static void vring_unmap_one(const struct vring_virtqueue *vq,
-			    struct vring_desc *desc)
+static int vring_mapping_error(const struct vring_virtqueue *vq,
+			       dma_addr_t addr)
+{
+	if (!vring_use_dma_api(vq->vq.vdev))
+		return 0;
+
+	return dma_mapping_error(vring_dma_dev(vq), addr);
+}
+
+static void vring_unmap_one_split(const struct vring_virtqueue *vq,
+				  struct vring_desc *desc)
 {
 	u16 flags;
 
@@ -225,17 +279,9 @@ static void vring_unmap_one(const struct vring_virtqueue
*vq,
 	}
 }
 
-static int vring_mapping_error(const struct vring_virtqueue *vq,
-			       dma_addr_t addr)
-{
-	if (!vring_use_dma_api(vq->vq.vdev))
-		return 0;
-
-	return dma_mapping_error(vring_dma_dev(vq), addr);
-}
-
-static struct vring_desc *alloc_indirect(struct virtqueue *_vq,
-					 unsigned int total_sg, gfp_t gfp)
+static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
+					       unsigned int total_sg,
+					       gfp_t gfp)
 {
 	struct vring_desc *desc;
 	unsigned int i;
@@ -256,14 +302,14 @@ static struct vring_desc *alloc_indirect(struct virtqueue
*_vq,
 	return desc;
 }
 
-static inline int virtqueue_add(struct virtqueue *_vq,
-				struct scatterlist *sgs[],
-				unsigned int total_sg,
-				unsigned int out_sgs,
-				unsigned int in_sgs,
-				void *data,
-				void *ctx,
-				gfp_t gfp)
+static inline int virtqueue_add_split(struct virtqueue *_vq,
+				      struct scatterlist *sgs[],
+				      unsigned int total_sg,
+				      unsigned int out_sgs,
+				      unsigned int in_sgs,
+				      void *data,
+				      void *ctx,
+				      gfp_t gfp)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	struct scatterlist *sg;
@@ -299,10 +345,8 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 
 	head = vq->free_head;
 
-	/* If the host supports indirect descriptor tables, and we have multiple
-	 * buffers, then go indirect. FIXME: tune this threshold */
-	if (vq->indirect && total_sg > 1 && vq->vq.num_free)
-		desc = alloc_indirect(_vq, total_sg, gfp);
+	if (virtqueue_use_indirect(_vq, total_sg))
+		desc = alloc_indirect_split(_vq, total_sg, gfp);
 	else {
 		desc = NULL;
 		WARN_ON_ONCE(total_sg > vq->vring.num && !vq->indirect);
@@ -423,7 +467,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 	for (n = 0; n < total_sg; n++) {
 		if (i == err_idx)
 			break;
-		vring_unmap_one(vq, &desc[i]);
+		vring_unmap_one_split(vq, &desc[i]);
 		i = virtio16_to_cpu(_vq->vdev, vq->vring.desc[i].next);
 	}
 
@@ -434,6 +478,355 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 	return -EIO;
 }
 
+static bool virtqueue_kick_prepare_split(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	u16 new, old;
+	bool needs_kick;
+
+	START_USE(vq);
+	/* We need to expose available array entries before checking avail
+	 * event. */
+	virtio_mb(vq->weak_barriers);
+
+	old = vq->avail_idx_shadow - vq->num_added;
+	new = vq->avail_idx_shadow;
+	vq->num_added = 0;
+
+#ifdef DEBUG
+	if (vq->last_add_time_valid) {
+		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
+					      vq->last_add_time)) > 100);
+	}
+	vq->last_add_time_valid = false;
+#endif
+
+	if (vq->event) {
+		needs_kick = vring_need_event(virtio16_to_cpu(_vq->vdev,
vring_avail_event(&vq->vring)),
+					      new, old);
+	} else {
+		needs_kick = !(vq->vring.used->flags &
cpu_to_virtio16(_vq->vdev, VRING_USED_F_NO_NOTIFY));
+	}
+	END_USE(vq);
+	return needs_kick;
+}
+
+static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
+			     void **ctx)
+{
+	unsigned int i, j;
+	__virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
+
+	/* Clear data ptr. */
+	vq->desc_state[head].data = NULL;
+
+	/* Put back on free list: unmap first-level descriptors and find end */
+	i = head;
+
+	while (vq->vring.desc[i].flags & nextflag) {
+		vring_unmap_one_split(vq, &vq->vring.desc[i]);
+		i = virtio16_to_cpu(vq->vq.vdev, vq->vring.desc[i].next);
+		vq->vq.num_free++;
+	}
+
+	vring_unmap_one_split(vq, &vq->vring.desc[i]);
+	vq->vring.desc[i].next = cpu_to_virtio16(vq->vq.vdev, vq->free_head);
+	vq->free_head = head;
+
+	/* Plus final descriptor */
+	vq->vq.num_free++;
+
+	if (vq->indirect) {
+		struct vring_desc *indir_desc = vq->desc_state[head].indir_desc;
+		u32 len;
+
+		/* Free the indirect table, if any, now that it's unmapped. */
+		if (!indir_desc)
+			return;
+
+		len = virtio32_to_cpu(vq->vq.vdev, vq->vring.desc[head].len);
+
+		BUG_ON(!(vq->vring.desc[head].flags &
+			 cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT)));
+		BUG_ON(len == 0 || len % sizeof(struct vring_desc));
+
+		for (j = 0; j < len / sizeof(struct vring_desc); j++)
+			vring_unmap_one_split(vq, &indir_desc[j]);
+
+		kfree(indir_desc);
+		vq->desc_state[head].indir_desc = NULL;
+	} else if (ctx) {
+		*ctx = vq->desc_state[head].indir_desc;
+	}
+}
+
+static inline bool more_used_split(const struct vring_virtqueue *vq)
+{
+	return vq->last_used_idx != virtio16_to_cpu(vq->vq.vdev,
vq->vring.used->idx);
+}
+
+static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq,
+					 unsigned int *len,
+					 void **ctx)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	void *ret;
+	unsigned int i;
+	u16 last_used;
+
+	START_USE(vq);
+
+	if (unlikely(vq->broken)) {
+		END_USE(vq);
+		return NULL;
+	}
+
+	if (!more_used_split(vq)) {
+		pr_debug("No more buffers in queue\n");
+		END_USE(vq);
+		return NULL;
+	}
+
+	/* Only get used array entries after they have been exposed by host. */
+	virtio_rmb(vq->weak_barriers);
+
+	last_used = (vq->last_used_idx & (vq->vring.num - 1));
+	i = virtio32_to_cpu(_vq->vdev, vq->vring.used->ring[last_used].id);
+	*len = virtio32_to_cpu(_vq->vdev,
vq->vring.used->ring[last_used].len);
+
+	if (unlikely(i >= vq->vring.num)) {
+		BAD_RING(vq, "id %u out of range\n", i);
+		return NULL;
+	}
+	if (unlikely(!vq->desc_state[i].data)) {
+		BAD_RING(vq, "id %u is not a head!\n", i);
+		return NULL;
+	}
+
+	/* detach_buf_split clears data, so grab it now. */
+	ret = vq->desc_state[i].data;
+	detach_buf_split(vq, i, ctx);
+	vq->last_used_idx++;
+	/* If we expect an interrupt for the next entry, tell host
+	 * by writing event index and flush out the write before
+	 * the read in the next get_buf call. */
+	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
+		virtio_store_mb(vq->weak_barriers,
+				&vring_used_event(&vq->vring),
+				cpu_to_virtio16(_vq->vdev, vq->last_used_idx));
+
+#ifdef DEBUG
+	vq->last_add_time_valid = false;
+#endif
+
+	END_USE(vq);
+	return ret;
+}
+
+static void virtqueue_disable_cb_split(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {
+		vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
+		if (!vq->event)
+			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
+	}
+}
+
+static unsigned virtqueue_enable_cb_prepare_split(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	u16 last_used_idx;
+
+	START_USE(vq);
+
+	/* We optimistically turn back on interrupts, then check if there was
+	 * more to do. */
+	/* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
+	 * either clear the flags bit or point the event index at the next
+	 * entry. Always do both to keep code simple. */
+	if (vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) {
+		vq->avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT;
+		if (!vq->event)
+			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
+	}
+	vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev,
last_used_idx = vq->last_used_idx);
+	END_USE(vq);
+	return last_used_idx;
+}
+
+static bool virtqueue_poll_split(struct virtqueue *_vq, unsigned last_used_idx)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	virtio_mb(vq->weak_barriers);
+	return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev,
vq->vring.used->idx);
+}
+
+static bool virtqueue_enable_cb_delayed_split(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	u16 bufs;
+
+	START_USE(vq);
+
+	/* We optimistically turn back on interrupts, then check if there was
+	 * more to do. */
+	/* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
+	 * either clear the flags bit or point the event index at the next
+	 * entry. Always update the event index to keep code simple. */
+	if (vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) {
+		vq->avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT;
+		if (!vq->event)
+			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
+	}
+	/* TODO: tune this threshold */
+	bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4;
+
+	virtio_store_mb(vq->weak_barriers,
+			&vring_used_event(&vq->vring),
+			cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs));
+
+	if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->vring.used->idx) -
vq->last_used_idx) > bufs)) {
+		END_USE(vq);
+		return false;
+	}
+
+	END_USE(vq);
+	return true;
+}
+
+static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	unsigned int i;
+	void *buf;
+
+	START_USE(vq);
+
+	for (i = 0; i < vq->vring.num; i++) {
+		if (!vq->desc_state[i].data)
+			continue;
+		/* detach_buf clears data, so grab it now. */
+		buf = vq->desc_state[i].data;
+		detach_buf_split(vq, i, NULL);
+		vq->avail_idx_shadow--;
+		vq->vring.avail->idx = cpu_to_virtio16(_vq->vdev,
vq->avail_idx_shadow);
+		END_USE(vq);
+		return buf;
+	}
+	/* That should have freed everything. */
+	BUG_ON(vq->vq.num_free != vq->vring.num);
+
+	END_USE(vq);
+	return NULL;
+}
+
+/*
+ * The layout for the packed ring is a continuous chunk of memory
+ * which looks like this.
+ *
+ * struct vring_packed {
+ *	// The actual descriptors (16 bytes each)
+ *	struct vring_packed_desc desc[num];
+ *
+ *	// Padding to the next align boundary.
+ *	char pad[];
+ *
+ *	// Driver Event Suppression
+ *	struct vring_packed_desc_event driver;
+ *
+ *	// Device Event Suppression
+ *	struct vring_packed_desc_event device;
+ * };
+ */
+static inline void vring_init_packed(struct vring_packed *vr, unsigned int num,
+				     void *p, unsigned long align)
+{
+	vr->num = num;
+	vr->desc = p;
+	vr->driver = (void *)ALIGN(((uintptr_t)p +
+		sizeof(struct vring_packed_desc) * num), align);
+	vr->device = vr->driver + 1;
+}
+
+static inline unsigned vring_size_packed(unsigned int num, unsigned long align)
+{
+	return ((sizeof(struct vring_packed_desc) * num + align - 1)
+		& ~(align - 1)) + sizeof(struct vring_packed_desc_event) * 2;
+}
+
+static inline int virtqueue_add_packed(struct virtqueue *_vq,
+				       struct scatterlist *sgs[],
+				       unsigned int total_sg,
+				       unsigned int out_sgs,
+				       unsigned int in_sgs,
+				       void *data,
+				       void *ctx,
+				       gfp_t gfp)
+{
+	return -EIO;
+}
+
+static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
+{
+	return false;
+}
+
+static inline bool more_used_packed(const struct vring_virtqueue *vq)
+{
+	return false;
+}
+
+static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
+					  unsigned int *len,
+					  void **ctx)
+{
+	return NULL;
+}
+
+static void virtqueue_disable_cb_packed(struct virtqueue *_vq)
+{
+}
+
+static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq)
+{
+	return 0;
+}
+
+static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned
last_used_idx)
+{
+	return false;
+}
+
+static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
+{
+	return false;
+}
+
+static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
+{
+	return NULL;
+}
+
+static inline int virtqueue_add(struct virtqueue *_vq,
+				struct scatterlist *sgs[],
+				unsigned int total_sg,
+				unsigned int out_sgs,
+				unsigned int in_sgs,
+				void *data,
+				void *ctx,
+				gfp_t gfp)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	return vq->packed ? virtqueue_add_packed(_vq, sgs, total_sg, out_sgs,
+						 in_sgs, data, ctx, gfp) :
+			    virtqueue_add_split(_vq, sgs, total_sg, out_sgs,
+						in_sgs, data, ctx, gfp);
+}
+
 /**
  * virtqueue_add_sgs - expose buffers to other end
  * @vq: the struct virtqueue we're talking about.
@@ -550,34 +943,9 @@ EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_ctx);
 bool virtqueue_kick_prepare(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
-	u16 new, old;
-	bool needs_kick;
 
-	START_USE(vq);
-	/* We need to expose available array entries before checking avail
-	 * event. */
-	virtio_mb(vq->weak_barriers);
-
-	old = vq->avail_idx_shadow - vq->num_added;
-	new = vq->avail_idx_shadow;
-	vq->num_added = 0;
-
-#ifdef DEBUG
-	if (vq->last_add_time_valid) {
-		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
-					      vq->last_add_time)) > 100);
-	}
-	vq->last_add_time_valid = false;
-#endif
-
-	if (vq->event) {
-		needs_kick = vring_need_event(virtio16_to_cpu(_vq->vdev,
vring_avail_event(&vq->vring)),
-					      new, old);
-	} else {
-		needs_kick = !(vq->vring.used->flags &
cpu_to_virtio16(_vq->vdev, VRING_USED_F_NO_NOTIFY));
-	}
-	END_USE(vq);
-	return needs_kick;
+	return vq->packed ? virtqueue_kick_prepare_packed(_vq) :
+			    virtqueue_kick_prepare_split(_vq);
 }
 EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);
 
@@ -625,58 +993,9 @@ bool virtqueue_kick(struct virtqueue *vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_kick);
 
-static void detach_buf(struct vring_virtqueue *vq, unsigned int head,
-		       void **ctx)
-{
-	unsigned int i, j;
-	__virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
-
-	/* Clear data ptr. */
-	vq->desc_state[head].data = NULL;
-
-	/* Put back on free list: unmap first-level descriptors and find end */
-	i = head;
-
-	while (vq->vring.desc[i].flags & nextflag) {
-		vring_unmap_one(vq, &vq->vring.desc[i]);
-		i = virtio16_to_cpu(vq->vq.vdev, vq->vring.desc[i].next);
-		vq->vq.num_free++;
-	}
-
-	vring_unmap_one(vq, &vq->vring.desc[i]);
-	vq->vring.desc[i].next = cpu_to_virtio16(vq->vq.vdev, vq->free_head);
-	vq->free_head = head;
-
-	/* Plus final descriptor */
-	vq->vq.num_free++;
-
-	if (vq->indirect) {
-		struct vring_desc *indir_desc = vq->desc_state[head].indir_desc;
-		u32 len;
-
-		/* Free the indirect table, if any, now that it's unmapped. */
-		if (!indir_desc)
-			return;
-
-		len = virtio32_to_cpu(vq->vq.vdev, vq->vring.desc[head].len);
-
-		BUG_ON(!(vq->vring.desc[head].flags &
-			 cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT)));
-		BUG_ON(len == 0 || len % sizeof(struct vring_desc));
-
-		for (j = 0; j < len / sizeof(struct vring_desc); j++)
-			vring_unmap_one(vq, &indir_desc[j]);
-
-		kfree(indir_desc);
-		vq->desc_state[head].indir_desc = NULL;
-	} else if (ctx) {
-		*ctx = vq->desc_state[head].indir_desc;
-	}
-}
-
 static inline bool more_used(const struct vring_virtqueue *vq)
 {
-	return vq->last_used_idx != virtio16_to_cpu(vq->vq.vdev,
vq->vring.used->idx);
+	return vq->packed ? more_used_packed(vq) : more_used_split(vq);
 }
 
 /**
@@ -699,57 +1018,9 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq,
unsigned int *len,
 			    void **ctx)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
-	void *ret;
-	unsigned int i;
-	u16 last_used;
 
-	START_USE(vq);
-
-	if (unlikely(vq->broken)) {
-		END_USE(vq);
-		return NULL;
-	}
-
-	if (!more_used(vq)) {
-		pr_debug("No more buffers in queue\n");
-		END_USE(vq);
-		return NULL;
-	}
-
-	/* Only get used array entries after they have been exposed by host. */
-	virtio_rmb(vq->weak_barriers);
-
-	last_used = (vq->last_used_idx & (vq->vring.num - 1));
-	i = virtio32_to_cpu(_vq->vdev, vq->vring.used->ring[last_used].id);
-	*len = virtio32_to_cpu(_vq->vdev,
vq->vring.used->ring[last_used].len);
-
-	if (unlikely(i >= vq->vring.num)) {
-		BAD_RING(vq, "id %u out of range\n", i);
-		return NULL;
-	}
-	if (unlikely(!vq->desc_state[i].data)) {
-		BAD_RING(vq, "id %u is not a head!\n", i);
-		return NULL;
-	}
-
-	/* detach_buf clears data, so grab it now. */
-	ret = vq->desc_state[i].data;
-	detach_buf(vq, i, ctx);
-	vq->last_used_idx++;
-	/* If we expect an interrupt for the next entry, tell host
-	 * by writing event index and flush out the write before
-	 * the read in the next get_buf call. */
-	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
-		virtio_store_mb(vq->weak_barriers,
-				&vring_used_event(&vq->vring),
-				cpu_to_virtio16(_vq->vdev, vq->last_used_idx));
-
-#ifdef DEBUG
-	vq->last_add_time_valid = false;
-#endif
-
-	END_USE(vq);
-	return ret;
+	return vq->packed ? virtqueue_get_buf_ctx_packed(_vq, len, ctx) :
+			    virtqueue_get_buf_ctx_split(_vq, len, ctx);
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_buf_ctx);
 
@@ -771,12 +1042,10 @@ void virtqueue_disable_cb(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
-	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {
-		vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
-		if (!vq->event)
-			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
-	}
-
+	if (vq->packed)
+		virtqueue_disable_cb_packed(_vq);
+	else
+		virtqueue_disable_cb_split(_vq);
 }
 EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
 
@@ -795,23 +1064,9 @@ EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
 unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
-	u16 last_used_idx;
 
-	START_USE(vq);
-
-	/* We optimistically turn back on interrupts, then check if there was
-	 * more to do. */
-	/* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
-	 * either clear the flags bit or point the event index at the next
-	 * entry. Always do both to keep code simple. */
-	if (vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) {
-		vq->avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT;
-		if (!vq->event)
-			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
-	}
-	vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev,
last_used_idx = vq->last_used_idx);
-	END_USE(vq);
-	return last_used_idx;
+	return vq->packed ? virtqueue_enable_cb_prepare_packed(_vq) :
+			    virtqueue_enable_cb_prepare_split(_vq);
 }
 EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);
 
@@ -828,8 +1083,8 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned
last_used_idx)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
-	virtio_mb(vq->weak_barriers);
-	return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev,
vq->vring.used->idx);
+	return vq->packed ? virtqueue_poll_packed(_vq, last_used_idx) :
+			    virtqueue_poll_split(_vq, last_used_idx);
 }
 EXPORT_SYMBOL_GPL(virtqueue_poll);
 
@@ -867,34 +1122,9 @@ EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
 bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
-	u16 bufs;
 
-	START_USE(vq);
-
-	/* We optimistically turn back on interrupts, then check if there was
-	 * more to do. */
-	/* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
-	 * either clear the flags bit or point the event index at the next
-	 * entry. Always update the event index to keep code simple. */
-	if (vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) {
-		vq->avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT;
-		if (!vq->event)
-			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
-	}
-	/* TODO: tune this threshold */
-	bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4;
-
-	virtio_store_mb(vq->weak_barriers,
-			&vring_used_event(&vq->vring),
-			cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs));
-
-	if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->vring.used->idx) -
vq->last_used_idx) > bufs)) {
-		END_USE(vq);
-		return false;
-	}
-
-	END_USE(vq);
-	return true;
+	return vq->packed ? virtqueue_enable_cb_delayed_packed(_vq) :
+			    virtqueue_enable_cb_delayed_split(_vq);
 }
 EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
 
@@ -909,27 +1139,9 @@ EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
 void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
-	unsigned int i;
-	void *buf;
 
-	START_USE(vq);
-
-	for (i = 0; i < vq->vring.num; i++) {
-		if (!vq->desc_state[i].data)
-			continue;
-		/* detach_buf clears data, so grab it now. */
-		buf = vq->desc_state[i].data;
-		detach_buf(vq, i, NULL);
-		vq->avail_idx_shadow--;
-		vq->vring.avail->idx = cpu_to_virtio16(_vq->vdev,
vq->avail_idx_shadow);
-		END_USE(vq);
-		return buf;
-	}
-	/* That should have freed everything. */
-	BUG_ON(vq->vq.num_free != vq->vring.num);
-
-	END_USE(vq);
-	return NULL;
+	return vq->packed ? virtqueue_detach_unused_buf_packed(_vq) :
+			    virtqueue_detach_unused_buf_split(_vq);
 }
 EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
 
@@ -954,7 +1166,8 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
 EXPORT_SYMBOL_GPL(vring_interrupt);
 
 struct virtqueue *__vring_new_virtqueue(unsigned int index,
-					struct vring vring,
+					union vring_union vring,
+					bool packed,
 					struct virtio_device *vdev,
 					bool weak_barriers,
 					bool context,
@@ -962,19 +1175,22 @@ struct virtqueue *__vring_new_virtqueue(unsigned int
index,
 					void (*callback)(struct virtqueue *),
 					const char *name)
 {
-	unsigned int i;
 	struct vring_virtqueue *vq;
+	unsigned int num, i;
+	size_t size;
 
-	vq = kmalloc(sizeof(*vq) + vring.num * sizeof(struct vring_desc_state),
-		     GFP_KERNEL);
+	num = packed ? vring.vring_packed.num : vring.vring_split.num;
+	size = packed ? num * sizeof(struct vring_desc_state_packed) :
+			num * sizeof(struct vring_desc_state);
+
+	vq = kmalloc(sizeof(*vq) + size, GFP_KERNEL);
 	if (!vq)
 		return NULL;
 
-	vq->vring = vring;
 	vq->vq.callback = callback;
 	vq->vq.vdev = vdev;
 	vq->vq.name = name;
-	vq->vq.num_free = vring.num;
+	vq->vq.num_free = num;
 	vq->vq.index = index;
 	vq->we_own_ring = false;
 	vq->queue_dma_addr = 0;
@@ -983,9 +1199,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 	vq->weak_barriers = weak_barriers;
 	vq->broken = false;
 	vq->last_used_idx = 0;
-	vq->avail_flags_shadow = 0;
-	vq->avail_idx_shadow = 0;
 	vq->num_added = 0;
+	vq->packed = packed;
 	list_add_tail(&vq->vq.list, &vdev->vqs);
 #ifdef DEBUG
 	vq->in_use = false;
@@ -996,19 +1211,48 @@ struct virtqueue *__vring_new_virtqueue(unsigned int
index,
 		!context;
 	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
 
+	if (vq->packed) {
+		vq->vring_packed = vring.vring_packed;
+		vq->next_avail_idx = 0;
+		vq->avail_wrap_counter = 1;
+		vq->used_wrap_counter = 1;
+		vq->event_flags_shadow = 0;
+
+		memset(vq->desc_state_packed, 0,
+			num * sizeof(struct vring_desc_state_packed));
+
+		/* Put everything in free lists. */
+		vq->free_head = 0;
+		for (i = 0; i < num-1; i++)
+			vq->desc_state_packed[i].next = i + 1;
+	} else {
+		vq->vring = vring.vring_split;
+		vq->avail_flags_shadow = 0;
+		vq->avail_idx_shadow = 0;
+
+		/* Put everything in free lists. */
+		vq->free_head = 0;
+		for (i = 0; i < num-1; i++)
+			vq->vring.desc[i].next = cpu_to_virtio16(vdev, i + 1);
+
+		memset(vq->desc_state, 0,
+			num * sizeof(struct vring_desc_state));
+	}
+
 	/* No callback?  Tell other side not to bother us. */
 	if (!callback) {
-		vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
-		if (!vq->event)
-			vq->vring.avail->flags = cpu_to_virtio16(vdev,
vq->avail_flags_shadow);
+		if (packed) {
+			vq->event_flags_shadow = VRING_EVENT_F_DISABLE;
+			vq->vring_packed.driver->flags = cpu_to_virtio16(vdev,
+						vq->event_flags_shadow);
+		} else {
+			vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
+			if (!vq->event)
+				vq->vring.avail->flags = cpu_to_virtio16(vdev,
+						vq->avail_flags_shadow);
+		}
 	}
 
-	/* Put everything in free lists. */
-	vq->free_head = 0;
-	for (i = 0; i < vring.num-1; i++)
-		vq->vring.desc[i].next = cpu_to_virtio16(vdev, i + 1);
-	memset(vq->desc_state, 0, vring.num * sizeof(struct vring_desc_state));
-
 	return &vq->vq;
 }
 EXPORT_SYMBOL_GPL(__vring_new_virtqueue);
@@ -1055,6 +1299,12 @@ static void vring_free_queue(struct virtio_device *vdev,
size_t size,
 	}
 }
 
+static inline int
+__vring_size(unsigned int num, unsigned long align, bool packed)
+{
+	return packed ? vring_size_packed(num, align) : vring_size(num, align);
+}
+
 struct virtqueue *vring_create_virtqueue(
 	unsigned int index,
 	unsigned int num,
@@ -1071,7 +1321,8 @@ struct virtqueue *vring_create_virtqueue(
 	void *queue = NULL;
 	dma_addr_t dma_addr;
 	size_t queue_size_in_bytes;
-	struct vring vring;
+	union vring_union vring;
+	bool packed;
 
 	/* We assume num is a power of 2. */
 	if (num & (num - 1)) {
@@ -1079,9 +1330,13 @@ struct virtqueue *vring_create_virtqueue(
 		return NULL;
 	}
 
+	packed = virtio_has_feature(vdev, VIRTIO_F_RING_PACKED);
+
 	/* TODO: allocate each queue chunk individually */
-	for (; num && vring_size(num, vring_align) > PAGE_SIZE; num /= 2) {
-		queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
+	for (; num && __vring_size(num, vring_align, packed) > PAGE_SIZE;
+			num /= 2) {
+		queue = vring_alloc_queue(vdev, __vring_size(num, vring_align,
+							     packed),
 					  &dma_addr,
 					  GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
 		if (queue)
@@ -1093,17 +1348,21 @@ struct virtqueue *vring_create_virtqueue(
 
 	if (!queue) {
 		/* Try to get a single page. You are my only hope! */
-		queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
+		queue = vring_alloc_queue(vdev, __vring_size(num, vring_align,
+							     packed),
 					  &dma_addr, GFP_KERNEL|__GFP_ZERO);
 	}
 	if (!queue)
 		return NULL;
 
-	queue_size_in_bytes = vring_size(num, vring_align);
-	vring_init(&vring, num, queue, vring_align);
+	queue_size_in_bytes = __vring_size(num, vring_align, packed);
+	if (packed)
+		vring_init_packed(&vring.vring_packed, num, queue, vring_align);
+	else
+		vring_init(&vring.vring_split, num, queue, vring_align);
 
-	vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
-				   notify, callback, name);
+	vq = __vring_new_virtqueue(index, vring, packed, vdev, weak_barriers,
+				   context, notify, callback, name);
 	if (!vq) {
 		vring_free_queue(vdev, queue_size_in_bytes, queue,
 				 dma_addr);
@@ -1129,10 +1388,17 @@ struct virtqueue *vring_new_virtqueue(unsigned int
index,
 				      void (*callback)(struct virtqueue *vq),
 				      const char *name)
 {
-	struct vring vring;
-	vring_init(&vring, num, pages, vring_align);
-	return __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
-				     notify, callback, name);
+	union vring_union vring;
+	bool packed;
+
+	packed = virtio_has_feature(vdev, VIRTIO_F_RING_PACKED);
+	if (packed)
+		vring_init_packed(&vring.vring_packed, num, pages, vring_align);
+	else
+		vring_init(&vring.vring_split, num, pages, vring_align);
+
+	return __vring_new_virtqueue(index, vring, packed, vdev, weak_barriers,
+				     context, notify, callback, name);
 }
 EXPORT_SYMBOL_GPL(vring_new_virtqueue);
 
@@ -1142,7 +1408,9 @@ void vring_del_virtqueue(struct virtqueue *_vq)
 
 	if (vq->we_own_ring) {
 		vring_free_queue(vq->vq.vdev, vq->queue_size_in_bytes,
-				 vq->vring.desc, vq->queue_dma_addr);
+				 vq->packed ? (void *)vq->vring_packed.desc :
+					      (void *)vq->vring.desc,
+				 vq->queue_dma_addr);
 	}
 	list_del(&_vq->list);
 	kfree(vq);
@@ -1184,7 +1452,7 @@ unsigned int virtqueue_get_vring_size(struct virtqueue
*_vq)
 
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
-	return vq->vring.num;
+	return vq->packed ? vq->vring_packed.num : vq->vring.num;
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_vring_size);
 
@@ -1227,6 +1495,10 @@ dma_addr_t virtqueue_get_avail_addr(struct virtqueue
*_vq)
 
 	BUG_ON(!vq->we_own_ring);
 
+	if (vq->packed)
+		return vq->queue_dma_addr + ((char *)vq->vring_packed.driver -
+				(char *)vq->vring_packed.desc);
+
 	return vq->queue_dma_addr +
 		((char *)vq->vring.avail - (char *)vq->vring.desc);
 }
@@ -1238,11 +1510,16 @@ dma_addr_t virtqueue_get_used_addr(struct virtqueue
*_vq)
 
 	BUG_ON(!vq->we_own_ring);
 
+	if (vq->packed)
+		return vq->queue_dma_addr + ((char *)vq->vring_packed.device -
+				(char *)vq->vring_packed.desc);
+
 	return vq->queue_dma_addr +
 		((char *)vq->vring.used - (char *)vq->vring.desc);
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_used_addr);
 
+/* Only available for split ring */
 const struct vring *virtqueue_get_vring(struct virtqueue *vq)
 {
 	return &to_vvq(vq)->vring;
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index fab02133a919..992142b35f55 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -60,6 +60,11 @@ static inline void virtio_store_mb(bool weak_barriers,
 struct virtio_device;
 struct virtqueue;
 
+union vring_union {
+	struct vring vring_split;
+	struct vring_packed vring_packed;
+};
+
 /*
  * Creates a virtqueue and allocates the descriptor ring.  If
  * may_reduce_num is set, then this may allocate a smaller ring than
@@ -79,7 +84,8 @@ struct virtqueue *vring_create_virtqueue(unsigned int index,
 
 /* Creates a virtqueue with a custom layout. */
 struct virtqueue *__vring_new_virtqueue(unsigned int index,
-					struct vring vring,
+					union vring_union vring,
+					bool packed,
 					struct virtio_device *vdev,
 					bool weak_barriers,
 					bool ctx,
-- 
2.18.0

This commit introduces the support (without EVENT_IDX) for
packed ring.

Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
---
 drivers/virtio/virtio_ring.c | 495 ++++++++++++++++++++++++++++++++++-
 1 file changed, 487 insertions(+), 8 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c4f8abc7445a..f317b485ba54 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -55,12 +55,21 @@
 #define END_USE(vq)
 #endif
 
+#define _VRING_DESC_F_AVAIL(b)	((__u16)(b) << 7)
+#define _VRING_DESC_F_USED(b)	((__u16)(b) << 15)
+
 struct vring_desc_state {
 	void *data;			/* Data for callback. */
 	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
 };
 
 struct vring_desc_state_packed {
+	void *data;			/* Data for callback. */
+	struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
+	int num;			/* Descriptor list length. */
+	dma_addr_t addr;		/* Buffer DMA addr. */
+	u32 len;			/* Buffer length. */
+	u16 flags;			/* Descriptor flags. */
 	int next;			/* The next desc state. */
 };
 
@@ -660,7 +669,6 @@ static bool virtqueue_poll_split(struct virtqueue *_vq,
unsigned last_used_idx)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
-	virtio_mb(vq->weak_barriers);
 	return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev,
vq->vring.used->idx);
 }
 
@@ -757,6 +765,72 @@ static inline unsigned vring_size_packed(unsigned int num,
unsigned long align)
 		& ~(align - 1)) + sizeof(struct vring_packed_desc_event) * 2;
 }
 
+static void vring_unmap_state_packed(const struct vring_virtqueue *vq,
+				     struct vring_desc_state_packed *state)
+{
+	u16 flags;
+
+	if (!vring_use_dma_api(vq->vq.vdev))
+		return;
+
+	flags = state->flags;
+
+	if (flags & VRING_DESC_F_INDIRECT) {
+		dma_unmap_single(vring_dma_dev(vq),
+				 state->addr, state->len,
+				 (flags & VRING_DESC_F_WRITE) ?
+				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
+	} else {
+		dma_unmap_page(vring_dma_dev(vq),
+			       state->addr, state->len,
+			       (flags & VRING_DESC_F_WRITE) ?
+			       DMA_FROM_DEVICE : DMA_TO_DEVICE);
+	}
+}
+
+static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
+				   struct vring_packed_desc *desc)
+{
+	u16 flags;
+
+	if (!vring_use_dma_api(vq->vq.vdev))
+		return;
+
+	flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
+
+	if (flags & VRING_DESC_F_INDIRECT) {
+		dma_unmap_single(vring_dma_dev(vq),
+				 virtio64_to_cpu(vq->vq.vdev, desc->addr),
+				 virtio32_to_cpu(vq->vq.vdev, desc->len),
+				 (flags & VRING_DESC_F_WRITE) ?
+				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
+	} else {
+		dma_unmap_page(vring_dma_dev(vq),
+			       virtio64_to_cpu(vq->vq.vdev, desc->addr),
+			       virtio32_to_cpu(vq->vq.vdev, desc->len),
+			       (flags & VRING_DESC_F_WRITE) ?
+			       DMA_FROM_DEVICE : DMA_TO_DEVICE);
+	}
+}
+
+static struct vring_packed_desc *alloc_indirect_packed(struct virtqueue *_vq,
+						       unsigned int total_sg,
+						       gfp_t gfp)
+{
+	struct vring_packed_desc *desc;
+
+	/*
+	 * We require lowmem mappings for the descriptors because
+	 * otherwise virt_to_phys will give us bogus addresses in the
+	 * virtqueue.
+	 */
+	gfp &= ~__GFP_HIGHMEM;
+
+	desc = kmalloc(total_sg * sizeof(struct vring_packed_desc), gfp);
+
+	return desc;
+}
+
 static inline int virtqueue_add_packed(struct virtqueue *_vq,
 				       struct scatterlist *sgs[],
 				       unsigned int total_sg,
@@ -766,47 +840,449 @@ static inline int virtqueue_add_packed(struct virtqueue
*_vq,
 				       void *ctx,
 				       gfp_t gfp)
 {
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	struct vring_packed_desc *desc;
+	struct scatterlist *sg;
+	unsigned int i, n, descs_used, uninitialized_var(prev), err_idx;
+	__virtio16 uninitialized_var(head_flags), flags;
+	u16 head, avail_wrap_counter, id, curr;
+	bool indirect;
+
+	START_USE(vq);
+
+	BUG_ON(data == NULL);
+	BUG_ON(ctx && vq->indirect);
+
+	if (unlikely(vq->broken)) {
+		END_USE(vq);
+		return -EIO;
+	}
+
+#ifdef DEBUG
+	{
+		ktime_t now = ktime_get();
+
+		/* No kick or get, with .1 second between?  Warn. */
+		if (vq->last_add_time_valid)
+			WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time))
+					    > 100);
+		vq->last_add_time = now;
+		vq->last_add_time_valid = true;
+	}
+#endif
+
+	BUG_ON(total_sg == 0);
+
+	head = vq->next_avail_idx;
+	avail_wrap_counter = vq->avail_wrap_counter;
+
+	if (virtqueue_use_indirect(_vq, total_sg))
+		desc = alloc_indirect_packed(_vq, total_sg, gfp);
+	else {
+		desc = NULL;
+		WARN_ON_ONCE(total_sg > vq->vring_packed.num &&
!vq->indirect);
+	}
+
+	if (desc) {
+		/* Use a single buffer which doesn't continue */
+		indirect = true;
+		/* Set up rest to use this indirect table. */
+		i = 0;
+		descs_used = 1;
+	} else {
+		indirect = false;
+		desc = vq->vring_packed.desc;
+		i = head;
+		descs_used = total_sg;
+	}
+
+	if (vq->vq.num_free < descs_used) {
+		pr_debug("Can't add buf len %i - avail = %i\n",
+			 descs_used, vq->vq.num_free);
+		/* FIXME: for historical reasons, we force a notify here if
+		 * there are outgoing parts to the buffer.  Presumably the
+		 * host should service the ring ASAP. */
+		if (out_sgs)
+			vq->notify(&vq->vq);
+		if (indirect)
+			kfree(desc);
+		END_USE(vq);
+		return -ENOSPC;
+	}
+
+	id = vq->free_head;
+	BUG_ON(id == vq->vring_packed.num);
+
+	curr = id;
+	for (n = 0; n < out_sgs + in_sgs; n++) {
+		for (sg = sgs[n]; sg; sg = sg_next(sg)) {
+			dma_addr_t addr = vring_map_one_sg(vq, sg, n < out_sgs ?
+					       DMA_TO_DEVICE : DMA_FROM_DEVICE);
+			if (vring_mapping_error(vq, addr))
+				goto unmap_release;
+
+			flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT |
+				  (n < out_sgs ? 0 : VRING_DESC_F_WRITE) |
+				  _VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
+				  _VRING_DESC_F_USED(!vq->avail_wrap_counter));
+			if (!indirect && i == head)
+				head_flags = flags;
+			else
+				desc[i].flags = flags;
+
+			desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
+			desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
+			i++;
+			if (!indirect) {
+				if (vring_use_dma_api(_vq->vdev)) {
+					vq->desc_state_packed[curr].addr = addr;
+					vq->desc_state_packed[curr].len +						sg->length;
+					vq->desc_state_packed[curr].flags +						virtio16_to_cpu(_vq->vdev,
+								flags);
+				}
+				curr = vq->desc_state_packed[curr].next;
+
+				if (i >= vq->vring_packed.num) {
+					i = 0;
+					vq->avail_wrap_counter ^= 1;
+				}
+			}
+		}
+	}
+
+	prev = (i > 0 ? i : vq->vring_packed.num) - 1;
+	desc[prev].id = cpu_to_virtio16(_vq->vdev, id);
+
+	/* Last one doesn't continue. */
+	if (total_sg == 1)
+		head_flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);
+	else
+		desc[prev].flags &= cpu_to_virtio16(_vq->vdev,
+						~VRING_DESC_F_NEXT);
+
+	if (indirect) {
+		/* Now that the indirect table is filled in, map it. */
+		dma_addr_t addr = vring_map_single(
+			vq, desc, total_sg * sizeof(struct vring_packed_desc),
+			DMA_TO_DEVICE);
+		if (vring_mapping_error(vq, addr))
+			goto unmap_release;
+
+		head_flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_INDIRECT |
+				      _VRING_DESC_F_AVAIL(avail_wrap_counter) |
+				      _VRING_DESC_F_USED(!avail_wrap_counter));
+		vq->vring_packed.desc[head].addr = cpu_to_virtio64(_vq->vdev,
+								   addr);
+		vq->vring_packed.desc[head].len = cpu_to_virtio32(_vq->vdev,
+				total_sg * sizeof(struct vring_packed_desc));
+		vq->vring_packed.desc[head].id = cpu_to_virtio16(_vq->vdev, id);
+
+		if (vring_use_dma_api(_vq->vdev)) {
+			vq->desc_state_packed[id].addr = addr;
+			vq->desc_state_packed[id].len = total_sg *
+					sizeof(struct vring_packed_desc);
+			vq->desc_state_packed[id].flags +					virtio16_to_cpu(_vq->vdev,
head_flags);
+		}
+	}
+
+	/* We're using some buffers from the free list. */
+	vq->vq.num_free -= descs_used;
+
+	/* Update free pointer */
+	if (indirect) {
+		n = head + 1;
+		if (n >= vq->vring_packed.num) {
+			n = 0;
+			vq->avail_wrap_counter ^= 1;
+		}
+		vq->next_avail_idx = n;
+		vq->free_head = vq->desc_state_packed[id].next;
+	} else {
+		vq->next_avail_idx = i;
+		vq->free_head = curr;
+	}
+
+	/* Store token and indirect buffer state. */
+	vq->desc_state_packed[id].num = descs_used;
+	vq->desc_state_packed[id].data = data;
+	if (indirect)
+		vq->desc_state_packed[id].indir_desc = desc;
+	else
+		vq->desc_state_packed[id].indir_desc = ctx;
+
+	/* A driver MUST NOT make the first descriptor in the list
+	 * available before all subsequent descriptors comprising
+	 * the list are made available. */
+	virtio_wmb(vq->weak_barriers);
+	vq->vring_packed.desc[head].flags = head_flags;
+	vq->num_added += descs_used;
+
+	pr_debug("Added buffer head %i to %p\n", head, vq);
+	END_USE(vq);
+
+	return 0;
+
+unmap_release:
+	err_idx = i;
+	i = head;
+
+	for (n = 0; n < total_sg; n++) {
+		if (i == err_idx)
+			break;
+		vring_unmap_desc_packed(vq, &desc[i]);
+		i++;
+		if (!indirect && i >= vq->vring_packed.num)
+			i = 0;
+	}
+
+	vq->avail_wrap_counter = avail_wrap_counter;
+
+	if (indirect)
+		kfree(desc);
+
+	END_USE(vq);
 	return -EIO;
 }
 
 static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
 {
-	return false;
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	u16 flags;
+	bool needs_kick;
+	u32 snapshot;
+
+	START_USE(vq);
+	/* We need to expose the new flags value before checking notification
+	 * suppressions. */
+	virtio_mb(vq->weak_barriers);
+
+	snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device);
+	flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16))
& 0x3;
+
+#ifdef DEBUG
+	if (vq->last_add_time_valid) {
+		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
+					      vq->last_add_time)) > 100);
+	}
+	vq->last_add_time_valid = false;
+#endif
+
+	needs_kick = (flags != VRING_EVENT_F_DISABLE);
+	END_USE(vq);
+	return needs_kick;
+}
+
+static void detach_buf_packed(struct vring_virtqueue *vq,
+			      unsigned int id, void **ctx)
+{
+	struct vring_desc_state_packed *state = NULL;
+	struct vring_packed_desc *desc;
+	unsigned int curr, i;
+
+	/* Clear data ptr. */
+	vq->desc_state_packed[id].data = NULL;
+
+	curr = id;
+	for (i = 0; i < vq->desc_state_packed[id].num; i++) {
+		state = &vq->desc_state_packed[curr];
+		vring_unmap_state_packed(vq, state);
+		curr = state->next;
+	}
+
+	BUG_ON(state == NULL);
+	vq->vq.num_free += vq->desc_state_packed[id].num;
+	state->next = vq->free_head;
+	vq->free_head = id;
+
+	if (vq->indirect) {
+		u32 len;
+
+		/* Free the indirect table, if any, now that it's unmapped. */
+		desc = vq->desc_state_packed[id].indir_desc;
+		if (!desc)
+			return;
+
+		if (vring_use_dma_api(vq->vq.vdev)) {
+			len = vq->desc_state_packed[id].len;
+			for (i = 0; i < len / sizeof(struct vring_packed_desc);
+					i++)
+				vring_unmap_desc_packed(vq, &desc[i]);
+		}
+		kfree(desc);
+		vq->desc_state_packed[id].indir_desc = NULL;
+	} else if (ctx) {
+		*ctx = vq->desc_state_packed[id].indir_desc;
+	}
+}
+
+static inline bool is_used_desc_packed(const struct vring_virtqueue *vq,
+				       u16 idx, bool used_wrap_counter)
+{
+	u16 flags;
+	bool avail, used;
+
+	flags = virtio16_to_cpu(vq->vq.vdev,
+				vq->vring_packed.desc[idx].flags);
+	avail = !!(flags & VRING_DESC_F_AVAIL);
+	used = !!(flags & VRING_DESC_F_USED);
+
+	return avail == used && used == used_wrap_counter;
 }
 
 static inline bool more_used_packed(const struct vring_virtqueue *vq)
 {
-	return false;
+	return is_used_desc_packed(vq, vq->last_used_idx,
+			vq->used_wrap_counter);
 }
 
 static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
 					  unsigned int *len,
 					  void **ctx)
 {
-	return NULL;
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	u16 last_used, id;
+	void *ret;
+
+	START_USE(vq);
+
+	if (unlikely(vq->broken)) {
+		END_USE(vq);
+		return NULL;
+	}
+
+	if (!more_used_packed(vq)) {
+		pr_debug("No more buffers in queue\n");
+		END_USE(vq);
+		return NULL;
+	}
+
+	/* Only get used elements after they have been exposed by host. */
+	virtio_rmb(vq->weak_barriers);
+
+	last_used = vq->last_used_idx;
+	id = virtio16_to_cpu(_vq->vdev, vq->vring_packed.desc[last_used].id);
+	*len = virtio32_to_cpu(_vq->vdev, vq->vring_packed.desc[last_used].len);
+
+	if (unlikely(id >= vq->vring_packed.num)) {
+		BAD_RING(vq, "id %u out of range\n", id);
+		return NULL;
+	}
+	if (unlikely(!vq->desc_state_packed[id].data)) {
+		BAD_RING(vq, "id %u is not a head!\n", id);
+		return NULL;
+	}
+
+	vq->last_used_idx += vq->desc_state_packed[id].num;
+	if (vq->last_used_idx >= vq->vring_packed.num) {
+		vq->last_used_idx -= vq->vring_packed.num;
+		vq->used_wrap_counter ^= 1;
+	}
+
+	/* detach_buf_packed clears data, so grab it now. */
+	ret = vq->desc_state_packed[id].data;
+	detach_buf_packed(vq, id, ctx);
+
+#ifdef DEBUG
+	vq->last_add_time_valid = false;
+#endif
+
+	END_USE(vq);
+	return ret;
 }
 
 static void virtqueue_disable_cb_packed(struct virtqueue *_vq)
 {
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	if (vq->event_flags_shadow != VRING_EVENT_F_DISABLE) {
+		vq->event_flags_shadow = VRING_EVENT_F_DISABLE;
+		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
+							vq->event_flags_shadow);
+	}
 }
 
 static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq)
 {
-	return 0;
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	START_USE(vq);
+
+	/* We optimistically turn back on interrupts, then check if there was
+	 * more to do. */
+
+	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
+		vq->event_flags_shadow = VRING_EVENT_F_ENABLE;
+		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
+							vq->event_flags_shadow);
+	}
+
+	END_USE(vq);
+	return vq->last_used_idx | ((u16)vq->used_wrap_counter << 15);
 }
 
-static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned
last_used_idx)
+static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned off_wrap)
 {
-	return false;
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	bool wrap_counter;
+	u16 used_idx;
+
+	wrap_counter = off_wrap >> 15;
+	used_idx = off_wrap & ~(1 << 15);
+
+	return is_used_desc_packed(vq, used_idx, wrap_counter);
 }
 
 static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
 {
-	return false;
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	START_USE(vq);
+
+	/* We optimistically turn back on interrupts, then check if there was
+	 * more to do. */
+
+	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
+		vq->event_flags_shadow = VRING_EVENT_F_ENABLE;
+		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
+							vq->event_flags_shadow);
+		/* We need to enable interrupts first before re-checking
+		 * for more used buffers. */
+		virtio_mb(vq->weak_barriers);
+	}
+
+	if (more_used_packed(vq)) {
+		END_USE(vq);
+		return false;
+	}
+
+	END_USE(vq);
+	return true;
 }
 
 static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
 {
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	unsigned int i;
+	void *buf;
+
+	START_USE(vq);
+
+	for (i = 0; i < vq->vring_packed.num; i++) {
+		if (!vq->desc_state_packed[i].data)
+			continue;
+		/* detach_buf clears data, so grab it now. */
+		buf = vq->desc_state_packed[i].data;
+		detach_buf_packed(vq, i, NULL);
+		END_USE(vq);
+		return buf;
+	}
+	/* That should have freed everything. */
+	BUG_ON(vq->vq.num_free != vq->vring_packed.num);
+
+	END_USE(vq);
 	return NULL;
 }
 
@@ -1083,6 +1559,9 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned
last_used_idx)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
+	/* We need to enable interrupts first before re-checking
+	 * for more used buffers. */
+	virtio_mb(vq->weak_barriers);
 	return vq->packed ? virtqueue_poll_packed(_vq, last_used_idx) :
 			    virtqueue_poll_split(_vq, last_used_idx);
 }
-- 
2.18.0

This commit introduces the EVENT_IDX support in packed ring.

Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
---
 drivers/virtio/virtio_ring.c | 73 ++++++++++++++++++++++++++++++++----
 1 file changed, 65 insertions(+), 8 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index f317b485ba54..f79a1e17f7d1 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1050,7 +1050,7 @@ static inline int virtqueue_add_packed(struct virtqueue
*_vq,
 static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
-	u16 flags;
+	u16 new, old, off_wrap, flags, wrap_counter, event_idx;
 	bool needs_kick;
 	u32 snapshot;
 
@@ -1059,9 +1059,19 @@ static bool virtqueue_kick_prepare_packed(struct
virtqueue *_vq)
 	 * suppressions. */
 	virtio_mb(vq->weak_barriers);
 
+	old = vq->next_avail_idx - vq->num_added;
+	new = vq->next_avail_idx;
+	vq->num_added = 0;
+
 	snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device);
+	off_wrap = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot & 0xffff));
 	flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16))
& 0x3;
 
+	wrap_counter = off_wrap >> 15;
+	event_idx = off_wrap & ~(1 << 15);
+	if (wrap_counter != vq->avail_wrap_counter)
+		event_idx -= vq->vring_packed.num;
+
 #ifdef DEBUG
 	if (vq->last_add_time_valid) {
 		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
@@ -1070,7 +1080,10 @@ static bool virtqueue_kick_prepare_packed(struct
virtqueue *_vq)
 	vq->last_add_time_valid = false;
 #endif
 
-	needs_kick = (flags != VRING_EVENT_F_DISABLE);
+	if (flags == VRING_EVENT_F_DESC)
+		needs_kick = vring_need_event(event_idx, new, old);
+	else
+		needs_kick = (flags != VRING_EVENT_F_DISABLE);
 	END_USE(vq);
 	return needs_kick;
 }
@@ -1185,6 +1198,15 @@ static void *virtqueue_get_buf_ctx_packed(struct
virtqueue *_vq,
 	ret = vq->desc_state_packed[id].data;
 	detach_buf_packed(vq, id, ctx);
 
+	/* If we expect an interrupt for the next entry, tell host
+	 * by writing event index and flush out the write before
+	 * the read in the next get_buf call. */
+	if (vq->event_flags_shadow == VRING_EVENT_F_DESC)
+		virtio_store_mb(vq->weak_barriers,
+				&vq->vring_packed.driver->off_wrap,
+				cpu_to_virtio16(_vq->vdev, vq->last_used_idx |
+					((u16)vq->used_wrap_counter << 15)));
+
 #ifdef DEBUG
 	vq->last_add_time_valid = false;
 #endif
@@ -1213,8 +1235,18 @@ static unsigned virtqueue_enable_cb_prepare_packed(struct
virtqueue *_vq)
 	/* We optimistically turn back on interrupts, then check if there was
 	 * more to do. */
 
+	if (vq->event) {
+		vq->vring_packed.driver->off_wrap = cpu_to_virtio16(_vq->vdev,
+				vq->last_used_idx |
+				((u16)vq->used_wrap_counter << 15));
+		/* We need to update event offset and event wrap
+		 * counter first before updating event flags. */
+		virtio_wmb(vq->weak_barriers);
+	}
+
 	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
-		vq->event_flags_shadow = VRING_EVENT_F_ENABLE;
+		vq->event_flags_shadow = vq->event ? VRING_EVENT_F_DESC :
+						     VRING_EVENT_F_ENABLE;
 		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
 							vq->event_flags_shadow);
 	}
@@ -1238,22 +1270,47 @@ static bool virtqueue_poll_packed(struct virtqueue *_vq,
unsigned off_wrap)
 static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
+	u16 bufs, used_idx, wrap_counter;
 
 	START_USE(vq);
 
 	/* We optimistically turn back on interrupts, then check if there was
 	 * more to do. */
 
+	if (vq->event) {
+		/* TODO: tune this threshold */
+		bufs = (vq->vring_packed.num - _vq->num_free) * 3 / 4;
+		wrap_counter = vq->used_wrap_counter;
+
+		used_idx = vq->last_used_idx + bufs;
+		if (used_idx >= vq->vring_packed.num) {
+			used_idx -= vq->vring_packed.num;
+			wrap_counter ^= 1;
+		}
+
+		vq->vring_packed.driver->off_wrap = cpu_to_virtio16(_vq->vdev,
+				used_idx | (wrap_counter << 15));
+
+		/* We need to update event offset and event wrap
+		 * counter first before updating event flags. */
+		virtio_wmb(vq->weak_barriers);
+	} else {
+		used_idx = vq->last_used_idx;
+		wrap_counter = vq->used_wrap_counter;
+	}
+
 	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
-		vq->event_flags_shadow = VRING_EVENT_F_ENABLE;
+		vq->event_flags_shadow = vq->event ? VRING_EVENT_F_DESC :
+						     VRING_EVENT_F_ENABLE;
 		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
 							vq->event_flags_shadow);
-		/* We need to enable interrupts first before re-checking
-		 * for more used buffers. */
-		virtio_mb(vq->weak_barriers);
 	}
 
-	if (more_used_packed(vq)) {
+	/* We need to update event suppression structure first
+	 * before re-checking for more used buffers. */
+	virtio_mb(vq->weak_barriers);
+
+	if (is_used_desc_packed(vq, used_idx, wrap_counter)) {
 		END_USE(vq);
 		return false;
 	}
-- 
2.18.0

Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
---
 drivers/s390/virtio/virtio_ccw.c | 14 ++++++++++++++
 drivers/virtio/virtio_ring.c     |  2 ++
 2 files changed, 16 insertions(+)

diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
index 8f5c1d7f751a..8654f3a94635 100644
--- a/drivers/s390/virtio/virtio_ccw.c
+++ b/drivers/s390/virtio/virtio_ccw.c
@@ -765,6 +765,17 @@ static u64 virtio_ccw_get_features(struct virtio_device
*vdev)
 	return rc;
 }
 
+static void ccw_transport_features(struct virtio_device *vdev)
+{
+	/*
+	 * Packed ring isn't enabled on virtio_ccw for now,
+	 * because virtio_ccw uses some legacy accessors,
+	 * e.g. virtqueue_get_avail() and virtqueue_get_used()
+	 * which aren't available in packed ring currently.
+	 */
+	__virtio_clear_bit(vdev, VIRTIO_F_RING_PACKED);
+}
+
 static int virtio_ccw_finalize_features(struct virtio_device *vdev)
 {
 	struct virtio_ccw_device *vcdev = to_vc_device(vdev);
@@ -791,6 +802,9 @@ static int virtio_ccw_finalize_features(struct virtio_device
*vdev)
 	/* Give virtio_ring a chance to accept features. */
 	vring_transport_features(vdev);
 
+	/* Give virtio_ccw a chance to accept features. */
+	ccw_transport_features(vdev);
+
 	features->index = 0;
 	features->features = cpu_to_le32((u32)vdev->features);
 	/* Write the first half of the feature bits to the host. */
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index f79a1e17f7d1..807ed4b362c5 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1968,6 +1968,8 @@ void vring_transport_features(struct virtio_device *vdev)
 			break;
 		case VIRTIO_F_IOMMU_PLATFORM:
 			break;
+		case VIRTIO_F_RING_PACKED:
+			break;
 		default:
 			/* We don't understand this bit. */
 			__virtio_clear_bit(vdev, i);
-- 
2.18.0

On 2018?07?11? 10:27, Tiwei Bie wrote:
> Hello everyone,
>
> This patch set implements packed ring support in virtio driver.
>
> Some functional tests have been done with Jason's
> packed ring implementation in vhost:
>
> https://lkml.org/lkml/2018/7/3/33
>
> Both of ping and netperf worked as expected.
>
> v1 -> v2:
> - Use READ_ONCE() to read event off_wrap and flags together (Jason);
> - Add comments related to ccw (Jason);
>
> RFC (v6) -> v1:
> - Avoid extra virtio_wmb() in virtqueue_enable_cb_delayed_packed()
>    when event idx is off (Jason);
> - Fix bufs calculation in virtqueue_enable_cb_delayed_packed() (Jason);
> - Test the state of the desc at used_idx instead of last_used_idx
>    in virtqueue_enable_cb_delayed_packed() (Jason);
> - Save wrap counter (as part of queue state) in the return value
>    of virtqueue_enable_cb_prepare_packed();
> - Refine the packed ring definitions in uapi;
> - Rebase on the net-next tree;
>
> RFC v5 -> RFC v6:
> - Avoid tracking addr/len/flags when DMA API isn't used (MST/Jason);
> - Define wrap counter as bool (Jason);
> - Use ALIGN() in vring_init_packed() (Jason);
> - Avoid using pointer to track `next` in detach_buf_packed() (Jason);
> - Add comments for barriers (Jason);
> - Don't enable RING_PACKED on ccw for now (noticed by Jason);
> - Refine the memory barrier in virtqueue_poll();
> - Add a missing memory barrier in virtqueue_enable_cb_delayed_packed();
> - Remove the hacks in virtqueue_enable_cb_prepare_packed();
>
> RFC v4 -> RFC v5:
> - Save DMA addr, etc in desc state (Jason);
> - Track used wrap counter;
>
> RFC v3 -> RFC v4:
> - Make ID allocation support out-of-order (Jason);
> - Various fixes for EVENT_IDX support;
>
> RFC v2 -> RFC v3:
> - Split into small patches (Jason);
> - Add helper virtqueue_use_indirect() (Jason);
> - Just set id for the last descriptor of a list (Jason);
> - Calculate the prev in virtqueue_add_packed() (Jason);
> - Fix/improve desc suppression code (Jason/MST);
> - Refine the code layout for XXX_split/packed and wrappers (MST);
> - Fix the comments and API in uapi (MST);
> - Remove the BUG_ON() for indirect (Jason);
> - Some other refinements and bug fixes;
>
> RFC v1 -> RFC v2:
> - Add indirect descriptor support - compile test only;
> - Add event suppression supprt - compile test only;
> - Move vring_packed_init() out of uapi (Jason, MST);
> - Merge two loops into one in virtqueue_add_packed() (Jason);
> - Split vring_unmap_one() for packed ring and split ring (Jason);
> - Avoid using '%' operator (Jason);
> - Rename free_head -> next_avail_idx (Jason);
> - Add comments for virtio_wmb() in virtqueue_add_packed() (Jason);
> - Some other refinements and bug fixes;
>
> Thanks!
>
> Tiwei Bie (5):
>    virtio: add packed ring definitions
>    virtio_ring: support creating packed ring
>    virtio_ring: add packed ring support
>    virtio_ring: add event idx support in packed ring
>    virtio_ring: enable packed ring
>
>   drivers/s390/virtio/virtio_ccw.c   |   14 +
>   drivers/virtio/virtio_ring.c       | 1365 ++++++++++++++++++++++------
>   include/linux/virtio_ring.h        |    8 +-
>   include/uapi/linux/virtio_config.h |    3 +
>   include/uapi/linux/virtio_ring.h   |   43 +
>   5 files changed, 1157 insertions(+), 276 deletions(-)
>
Acked-by: Jason Wang <jasowang at redhat.com>

Thanks!

From: Tiwei Bie <tiwei.bie at intel.com>
Date: Wed, 11 Jul 2018 10:27:06 +0800
> Hello everyone,
> 
> This patch set implements packed ring support in virtio driver.
> 
> Some functional tests have been done with Jason's
> packed ring implementation in vhost:
> 
> https://lkml.org/lkml/2018/7/3/33
> 
> Both of ping and netperf worked as expected.
Michael and Jason, where are we with this series?

On 2018?07?13? 05:44, David Miller wrote:
> From: Tiwei Bie <tiwei.bie at intel.com>
> Date: Wed, 11 Jul 2018 10:27:06 +0800
>
>> Hello everyone,
>>
>> This patch set implements packed ring support in virtio driver.
>>
>> Some functional tests have been done with Jason's
>> packed ring implementation in vhost:
>>
>> https://lkml.org/lkml/2018/7/3/33
>>
>> Both of ping and netperf worked as expected.
> Michael and Jason, where are we with this series?
For the series:

Acked-by: Jason Wang <jasowang at redhat.com>

On Thu, Jul 12, 2018 at 02:44:58PM -0700, David Miller
wrote:
> From: Tiwei Bie <tiwei.bie at intel.com>
> Date: Wed, 11 Jul 2018 10:27:06 +0800
> 
> > Hello everyone,
> > 
> > This patch set implements packed ring support in virtio driver.
> > 
> > Some functional tests have been done with Jason's
> > packed ring implementation in vhost:
> > 
> > https://lkml.org/lkml/2018/7/3/33
> > 
> > Both of ping and netperf worked as expected.
> 
> Michael and Jason, where are we with this series?
I'm at netdev, won't be able to review before Monday.

-- 
MST

On Wed, Jul 11, 2018 at 10:27:09AM +0800, Tiwei Bie
wrote:
> This commit introduces the support (without EVENT_IDX) for
> packed ring.
> 
> Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
> ---
>  drivers/virtio/virtio_ring.c | 495 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 487 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c4f8abc7445a..f317b485ba54 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -55,12 +55,21 @@
>  #define END_USE(vq)
>  #endif
>  
> +#define _VRING_DESC_F_AVAIL(b)	((__u16)(b) << 7)
> +#define _VRING_DESC_F_USED(b)	((__u16)(b) << 15)
Underscore followed by an upper case letter isn't a good idea
for a symbol. And it's not nice that this does not
use the VRING_DESC_F_USED from the header.
How about ((b) ? VRING_DESC_F_USED : 0) instead?
Is produced code worse then?
> +
>  struct vring_desc_state {
>  	void *data;			/* Data for callback. */
>  	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
>  };
>  
>  struct vring_desc_state_packed {
> +	void *data;			/* Data for callback. */
> +	struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
Include vring_desc_state for these?
> +	int num;			/* Descriptor list length. */
> +	dma_addr_t addr;		/* Buffer DMA addr. */
> +	u32 len;			/* Buffer length. */
> +	u16 flags;			/* Descriptor flags. */
This seems only to be used for indirect. Check indirect field above
instead and drop this.
>  	int next;			/* The next desc state. */
Packing things into 16 bit integers will help reduce
cache pressure here.

Also, this is only used for unmap, so when dma API is not used,
maintaining addr and len list management is unnecessary. How about we
maintain addr/len in a separate array, avoiding accesses on unmap in that case?

Also, lots of architectures have a nop unmap in the DMA API.
See a proposed patch at the end for optimizing that case.
>  };
>  
> @@ -660,7 +669,6 @@ static bool virtqueue_poll_split(struct virtqueue *_vq,
unsigned last_used_idx)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  
> -	virtio_mb(vq->weak_barriers);
>  	return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev,
vq->vring.used->idx);
>  }
why is this changing the split queue implementation?

>  
> @@ -757,6 +765,72 @@ static inline unsigned vring_size_packed(unsigned int
num, unsigned long align)
>  		& ~(align - 1)) + sizeof(struct vring_packed_desc_event) * 2;
>  }
>  
> +static void vring_unmap_state_packed(const struct vring_virtqueue *vq,
> +				     struct vring_desc_state_packed *state)
> +{
> +	u16 flags;
> +
> +	if (!vring_use_dma_api(vq->vq.vdev))
> +		return;
> +
> +	flags = state->flags;
> +
> +	if (flags & VRING_DESC_F_INDIRECT) {
> +		dma_unmap_single(vring_dma_dev(vq),
> +				 state->addr, state->len,
> +				 (flags & VRING_DESC_F_WRITE) ?
> +				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
> +	} else {
> +		dma_unmap_page(vring_dma_dev(vq),
> +			       state->addr, state->len,
> +			       (flags & VRING_DESC_F_WRITE) ?
> +			       DMA_FROM_DEVICE : DMA_TO_DEVICE);
> +	}
> +}
> +
> +static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
> +				   struct vring_packed_desc *desc)
> +{
> +	u16 flags;
> +
> +	if (!vring_use_dma_api(vq->vq.vdev))
> +		return;
> +
> +	flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
I see no reason to use virtioXX wrappers for the packed ring.
That's there to support legacy devices. Just use leXX.
> +
> +	if (flags & VRING_DESC_F_INDIRECT) {
> +		dma_unmap_single(vring_dma_dev(vq),
> +				 virtio64_to_cpu(vq->vq.vdev, desc->addr),
> +				 virtio32_to_cpu(vq->vq.vdev, desc->len),
> +				 (flags & VRING_DESC_F_WRITE) ?
> +				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
> +	} else {
> +		dma_unmap_page(vring_dma_dev(vq),
> +			       virtio64_to_cpu(vq->vq.vdev, desc->addr),
> +			       virtio32_to_cpu(vq->vq.vdev, desc->len),
> +			       (flags & VRING_DESC_F_WRITE) ?
> +			       DMA_FROM_DEVICE : DMA_TO_DEVICE);
> +	}
> +}
> +
> +static struct vring_packed_desc *alloc_indirect_packed(struct virtqueue
*_vq,
> +						       unsigned int total_sg,
> +						       gfp_t gfp)
> +{
> +	struct vring_packed_desc *desc;
> +
> +	/*
> +	 * We require lowmem mappings for the descriptors because
> +	 * otherwise virt_to_phys will give us bogus addresses in the
> +	 * virtqueue.
Where is virt_to_phys used? I don't see it in this patch.
> +	 */
> +	gfp &= ~__GFP_HIGHMEM;
> +
> +	desc = kmalloc(total_sg * sizeof(struct vring_packed_desc), gfp);
> +
> +	return desc;
> +}
> +
>  static inline int virtqueue_add_packed(struct virtqueue *_vq,
>  				       struct scatterlist *sgs[],
>  				       unsigned int total_sg,
> @@ -766,47 +840,449 @@ static inline int virtqueue_add_packed(struct
virtqueue *_vq,
>  				       void *ctx,
>  				       gfp_t gfp)
>  {
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	struct vring_packed_desc *desc;
> +	struct scatterlist *sg;
> +	unsigned int i, n, descs_used, uninitialized_var(prev), err_idx;
> +	__virtio16 uninitialized_var(head_flags), flags;
> +	u16 head, avail_wrap_counter, id, curr;
> +	bool indirect;
> +
> +	START_USE(vq);
> +
> +	BUG_ON(data == NULL);
> +	BUG_ON(ctx && vq->indirect);
> +
> +	if (unlikely(vq->broken)) {
> +		END_USE(vq);
> +		return -EIO;
> +	}
> +
> +#ifdef DEBUG
> +	{
> +		ktime_t now = ktime_get();
> +
> +		/* No kick or get, with .1 second between?  Warn. */
> +		if (vq->last_add_time_valid)
> +			WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time))
> +					    > 100);
> +		vq->last_add_time = now;
> +		vq->last_add_time_valid = true;
> +	}
> +#endif
Add incline helpers for this debug stuff rather than
duplicate it from split ring?

> +
> +	BUG_ON(total_sg == 0);
> +
> +	head = vq->next_avail_idx;
> +	avail_wrap_counter = vq->avail_wrap_counter;
> +
> +	if (virtqueue_use_indirect(_vq, total_sg))
> +		desc = alloc_indirect_packed(_vq, total_sg, gfp);
> +	else {
> +		desc = NULL;
> +		WARN_ON_ONCE(total_sg > vq->vring_packed.num &&
!vq->indirect);
> +	}

Apparently this attempts to treat indirect descriptors same as
direct ones. This is how it is in the split ring, but not in
the packed one. I think you want two separate functions, for
direct and indirect.
> +
> +	if (desc) {
> +		/* Use a single buffer which doesn't continue */
> +		indirect = true;
> +		/* Set up rest to use this indirect table. */
> +		i = 0;
> +		descs_used = 1;
> +	} else {
> +		indirect = false;
> +		desc = vq->vring_packed.desc;
> +		i = head;
> +		descs_used = total_sg;
> +	}
> +
> +	if (vq->vq.num_free < descs_used) {
> +		pr_debug("Can't add buf len %i - avail = %i\n",
> +			 descs_used, vq->vq.num_free);
> +		/* FIXME: for historical reasons, we force a notify here if
> +		 * there are outgoing parts to the buffer.  Presumably the
> +		 * host should service the ring ASAP. */
> +		if (out_sgs)
> +			vq->notify(&vq->vq);
> +		if (indirect)
> +			kfree(desc);
> +		END_USE(vq);
> +		return -ENOSPC;
> +	}
> +
> +	id = vq->free_head;
> +	BUG_ON(id == vq->vring_packed.num);
> +
> +	curr = id;
> +	for (n = 0; n < out_sgs + in_sgs; n++) {
> +		for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> +			dma_addr_t addr = vring_map_one_sg(vq, sg, n < out_sgs ?
> +					       DMA_TO_DEVICE : DMA_FROM_DEVICE);
> +			if (vring_mapping_error(vq, addr))
> +				goto unmap_release;
> +
> +			flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT |
> +				  (n < out_sgs ? 0 : VRING_DESC_F_WRITE) |
> +				  _VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
> +				  _VRING_DESC_F_USED(!vq->avail_wrap_counter));
Spec says:
	The VIRTQ_DESC_F_WRITE flags bit is the only valid flag for descriptors in the
	indirect table.

All this logic isn't needed for indirect.

Also, why re-calculate avail/used flags every time? They only change
when you wrap around.

> +			if (!indirect && i == head)
> +				head_flags = flags;
> +			else
> +				desc[i].flags = flags;
> +
> +			desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
> +			desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
> +			i++;
> +			if (!indirect) {
> +				if (vring_use_dma_api(_vq->vdev)) {
> +					vq->desc_state_packed[curr].addr = addr;
> +					vq->desc_state_packed[curr].len > +						sg->length;
> +					vq->desc_state_packed[curr].flags > +					
virtio16_to_cpu(_vq->vdev,
> +								flags);
> +				}
> +				curr = vq->desc_state_packed[curr].next;
> +
> +				if (i >= vq->vring_packed.num) {
> +					i = 0;
> +					vq->avail_wrap_counter ^= 1;
> +				}
> +			}
> +		}
> +	}
> +
> +	prev = (i > 0 ? i : vq->vring_packed.num) - 1;
> +	desc[prev].id = cpu_to_virtio16(_vq->vdev, id);
Is it easier to write this out in all descriptors, to avoid the need to
calculate prev?
> +
> +	/* Last one doesn't continue. */
> +	if (total_sg == 1)
> +		head_flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);
> +	else
> +		desc[prev].flags &= cpu_to_virtio16(_vq->vdev,
> +						~VRING_DESC_F_NEXT);
Wouldn't it be easier to avoid setting VRING_DESC_F_NEXT
in the first place?
	 if (n != in_sgs - 1 && n != out_sgs - 1)

must be better than writing descriptor an extra time.
> +
> +	if (indirect) {
> +		/* Now that the indirect table is filled in, map it. */
> +		dma_addr_t addr = vring_map_single(
> +			vq, desc, total_sg * sizeof(struct vring_packed_desc),
> +			DMA_TO_DEVICE);
> +		if (vring_mapping_error(vq, addr))
> +			goto unmap_release;
> +
> +		head_flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_INDIRECT |
> +				      _VRING_DESC_F_AVAIL(avail_wrap_counter) |
> +				      _VRING_DESC_F_USED(!avail_wrap_counter));
> +		vq->vring_packed.desc[head].addr = cpu_to_virtio64(_vq->vdev,
> +								   addr);
> +		vq->vring_packed.desc[head].len = cpu_to_virtio32(_vq->vdev,
> +				total_sg * sizeof(struct vring_packed_desc));
> +		vq->vring_packed.desc[head].id = cpu_to_virtio16(_vq->vdev, id);
> +
> +		if (vring_use_dma_api(_vq->vdev)) {
> +			vq->desc_state_packed[id].addr = addr;
> +			vq->desc_state_packed[id].len = total_sg *
> +					sizeof(struct vring_packed_desc);
> +			vq->desc_state_packed[id].flags > +				
virtio16_to_cpu(_vq->vdev, head_flags);
> +		}
> +	}
> +
> +	/* We're using some buffers from the free list. */
> +	vq->vq.num_free -= descs_used;
> +
> +	/* Update free pointer */
> +	if (indirect) {
> +		n = head + 1;
> +		if (n >= vq->vring_packed.num) {
> +			n = 0;
> +			vq->avail_wrap_counter ^= 1;
> +		}
> +		vq->next_avail_idx = n;
> +		vq->free_head = vq->desc_state_packed[id].next;
> +	} else {
> +		vq->next_avail_idx = i;
> +		vq->free_head = curr;
> +	}
> +
> +	/* Store token and indirect buffer state. */
> +	vq->desc_state_packed[id].num = descs_used;
> +	vq->desc_state_packed[id].data = data;
> +	if (indirect)
> +		vq->desc_state_packed[id].indir_desc = desc;
> +	else
> +		vq->desc_state_packed[id].indir_desc = ctx;
> +
> +	/* A driver MUST NOT make the first descriptor in the list
> +	 * available before all subsequent descriptors comprising
> +	 * the list are made available. */
> +	virtio_wmb(vq->weak_barriers);
> +	vq->vring_packed.desc[head].flags = head_flags;
> +	vq->num_added += descs_used;
> +
> +	pr_debug("Added buffer head %i to %p\n", head, vq);
> +	END_USE(vq);
> +
> +	return 0;
> +
> +unmap_release:
> +	err_idx = i;
> +	i = head;
> +
> +	for (n = 0; n < total_sg; n++) {
> +		if (i == err_idx)
> +			break;
> +		vring_unmap_desc_packed(vq, &desc[i]);
> +		i++;
> +		if (!indirect && i >= vq->vring_packed.num)
> +			i = 0;
> +	}
> +
> +	vq->avail_wrap_counter = avail_wrap_counter;
> +
> +	if (indirect)
> +		kfree(desc);
> +
> +	END_USE(vq);
>  	return -EIO;
>  }
>  
>  static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
>  {
> -	return false;
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 flags;
> +	bool needs_kick;
> +	u32 snapshot;
> +
> +	START_USE(vq);
> +	/* We need to expose the new flags value before checking notification
> +	 * suppressions. */
> +	virtio_mb(vq->weak_barriers);
> +
> +	snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device);
> +	flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16))
& 0x3;
What are all these hard-coded things? Also either we do READ_ONCE
everywhere or nowhere. Why is this place special? Any why read 32 bit
if you only want the 16?

And doesn't sparse complain about cast to __virtio16?
> +
> +#ifdef DEBUG
> +	if (vq->last_add_time_valid) {
> +		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
> +					      vq->last_add_time)) > 100);
> +	}
> +	vq->last_add_time_valid = false;
> +#endif
> +
> +	needs_kick = (flags != VRING_EVENT_F_DISABLE);
> +	END_USE(vq);
> +	return needs_kick;
> +}
> +
> +static void detach_buf_packed(struct vring_virtqueue *vq,
> +			      unsigned int id, void **ctx)
> +{
> +	struct vring_desc_state_packed *state = NULL;
> +	struct vring_packed_desc *desc;
> +	unsigned int curr, i;
> +
> +	/* Clear data ptr. */
> +	vq->desc_state_packed[id].data = NULL;
> +
> +	curr = id;
> +	for (i = 0; i < vq->desc_state_packed[id].num; i++) {
> +		state = &vq->desc_state_packed[curr];
> +		vring_unmap_state_packed(vq, state);
> +		curr = state->next;
> +	}
> +
> +	BUG_ON(state == NULL);
> +	vq->vq.num_free += vq->desc_state_packed[id].num;
> +	state->next = vq->free_head;
> +	vq->free_head = id;
> +
> +	if (vq->indirect) {
> +		u32 len;
> +
> +		/* Free the indirect table, if any, now that it's unmapped. */
> +		desc = vq->desc_state_packed[id].indir_desc;
> +		if (!desc)
> +			return;
> +
> +		if (vring_use_dma_api(vq->vq.vdev)) {
> +			len = vq->desc_state_packed[id].len;
> +			for (i = 0; i < len / sizeof(struct vring_packed_desc);
> +					i++)
> +				vring_unmap_desc_packed(vq, &desc[i]);
> +		}
> +		kfree(desc);
> +		vq->desc_state_packed[id].indir_desc = NULL;
> +	} else if (ctx) {
> +		*ctx = vq->desc_state_packed[id].indir_desc;
> +	}
> +}
> +
> +static inline bool is_used_desc_packed(const struct vring_virtqueue *vq,
> +				       u16 idx, bool used_wrap_counter)
> +{
> +	u16 flags;
> +	bool avail, used;
> +
> +	flags = virtio16_to_cpu(vq->vq.vdev,
> +				vq->vring_packed.desc[idx].flags);
> +	avail = !!(flags & VRING_DESC_F_AVAIL);
> +	used = !!(flags & VRING_DESC_F_USED);
> +
> +	return avail == used && used == used_wrap_counter;
I think that you don't need to look at avail flag to detect a used
descriptor. The reason device writes it is to avoid confusing
*device* next time descriptor wraps.
>  }
>  
>  static inline bool more_used_packed(const struct vring_virtqueue *vq)
>  {
> -	return false;
> +	return is_used_desc_packed(vq, vq->last_used_idx,
> +			vq->used_wrap_counter);
>  }
>  
>  static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
>  					  unsigned int *len,
>  					  void **ctx)
>  {
> -	return NULL;
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 last_used, id;
> +	void *ret;
> +
> +	START_USE(vq);
> +
> +	if (unlikely(vq->broken)) {
> +		END_USE(vq);
> +		return NULL;
> +	}
> +
> +	if (!more_used_packed(vq)) {
> +		pr_debug("No more buffers in queue\n");
> +		END_USE(vq);
> +		return NULL;
> +	}
> +
> +	/* Only get used elements after they have been exposed by host. */
> +	virtio_rmb(vq->weak_barriers);
> +
> +	last_used = vq->last_used_idx;
> +	id = virtio16_to_cpu(_vq->vdev,
vq->vring_packed.desc[last_used].id);
> +	*len = virtio32_to_cpu(_vq->vdev,
vq->vring_packed.desc[last_used].len);
> +
> +	if (unlikely(id >= vq->vring_packed.num)) {
> +		BAD_RING(vq, "id %u out of range\n", id);
> +		return NULL;
> +	}
> +	if (unlikely(!vq->desc_state_packed[id].data)) {
> +		BAD_RING(vq, "id %u is not a head!\n", id);
> +		return NULL;
> +	}
> +
> +	vq->last_used_idx += vq->desc_state_packed[id].num;
> +	if (vq->last_used_idx >= vq->vring_packed.num) {
> +		vq->last_used_idx -= vq->vring_packed.num;
> +		vq->used_wrap_counter ^= 1;
> +	}
> +
> +	/* detach_buf_packed clears data, so grab it now. */
> +	ret = vq->desc_state_packed[id].data;
> +	detach_buf_packed(vq, id, ctx);
> +
> +#ifdef DEBUG
> +	vq->last_add_time_valid = false;
> +#endif
> +
> +	END_USE(vq);
> +	return ret;
>  }
>  
>  static void virtqueue_disable_cb_packed(struct virtqueue *_vq)
>  {
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	if (vq->event_flags_shadow != VRING_EVENT_F_DISABLE) {
> +		vq->event_flags_shadow = VRING_EVENT_F_DISABLE;
> +		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
> +							vq->event_flags_shadow);
> +	}
>  }
>  
>  static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq)
>  {
> -	return 0;
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	START_USE(vq);
> +
> +	/* We optimistically turn back on interrupts, then check if there was
> +	 * more to do. */
> +
> +	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
> +		vq->event_flags_shadow = VRING_EVENT_F_ENABLE;
> +		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
> +							vq->event_flags_shadow);
> +	}
> +
> +	END_USE(vq);
> +	return vq->last_used_idx | ((u16)vq->used_wrap_counter <<
15);
>  }
>  
> -static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned
last_used_idx)
> +static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned
off_wrap)
>  {
> -	return false;
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	bool wrap_counter;
> +	u16 used_idx;
> +
> +	wrap_counter = off_wrap >> 15;
> +	used_idx = off_wrap & ~(1 << 15);
> +
> +	return is_used_desc_packed(vq, used_idx, wrap_counter);
These >> 15 << 15 all over the place duplicate info.
Pls put 15 in the header.

Also can you maintain the counters properly shifted?
Then just use them.

>  }
>  
>  static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
>  {
> -	return false;
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	START_USE(vq);
> +
> +	/* We optimistically turn back on interrupts, then check if there was
> +	 * more to do. */
> +
> +	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
> +		vq->event_flags_shadow = VRING_EVENT_F_ENABLE;
> +		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
> +							vq->event_flags_shadow);
> +		/* We need to enable interrupts first before re-checking
> +		 * for more used buffers. */
> +		virtio_mb(vq->weak_barriers);
> +	}
> +
> +	if (more_used_packed(vq)) {
> +		END_USE(vq);
> +		return false;
> +	}
> +
> +	END_USE(vq);
> +	return true;
>  }
>  
>  static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
>  {
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	unsigned int i;
> +	void *buf;
> +
> +	START_USE(vq);
> +
> +	for (i = 0; i < vq->vring_packed.num; i++) {
> +		if (!vq->desc_state_packed[i].data)
> +			continue;
> +		/* detach_buf clears data, so grab it now. */
> +		buf = vq->desc_state_packed[i].data;
> +		detach_buf_packed(vq, i, NULL);
> +		END_USE(vq);
> +		return buf;
> +	}
> +	/* That should have freed everything. */
> +	BUG_ON(vq->vq.num_free != vq->vring_packed.num);
> +
> +	END_USE(vq);
>  	return NULL;
>  }
>  
> @@ -1083,6 +1559,9 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned
last_used_idx)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  
> +	/* We need to enable interrupts first before re-checking
> +	 * for more used buffers. */
> +	virtio_mb(vq->weak_barriers);
>  	return vq->packed ? virtqueue_poll_packed(_vq, last_used_idx) :
>  			    virtqueue_poll_split(_vq, last_used_idx);
>  }
Possible optimization for when dma API is in use:

--->

dma: detecting nop unmap

drivers need to maintain the dma address for unmap purposes,
but these cycles are wasted when unmap callback is not
defined. Add an API for drivers to check that and avoid
unmap completely. Debug builds still have unmap.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>

----

diff --git a/include/linux/dma-debug.h b/include/linux/dma-debug.h
index a785f2507159..38b2c27c8449 100644
--- a/include/linux/dma-debug.h
+++ b/include/linux/dma-debug.h
@@ -42,6 +42,11 @@ extern void debug_dma_mapping_error(struct device *dev,
dma_addr_t dma_addr);
 extern void debug_dma_unmap_page(struct device *dev, dma_addr_t addr,
 				 size_t size, int direction, bool map_single);
 
+static inline bool has_debug_dma_unmap(struct device *dev)
+{
+	return true;
+}
+
 extern void debug_dma_map_sg(struct device *dev, struct scatterlist *sg,
 			     int nents, int mapped_ents, int direction);
 
@@ -121,6 +126,11 @@ static inline void debug_dma_unmap_page(struct device *dev,
dma_addr_t addr,
 {
 }
 
+static inline bool has_debug_dma_unmap(struct device *dev)
+{
+	return false;
+}
+
 static inline void debug_dma_map_sg(struct device *dev, struct scatterlist *sg,
 				    int nents, int mapped_ents, int direction)
 {
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 1db6a6b46d0d..656f3e518166 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -241,6 +241,14 @@ static inline dma_addr_t dma_map_single_attrs(struct device
*dev, void *ptr,
 	return addr;
 }
 
+static inline bool has_dma_unmap(struct device *dev)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	return ops->unmap_page || ops->unmap_sg || ops->unmap_resource ||
+		has_dma_unmap(dev);
+}
+
 static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
 					  size_t size,
 					  enum dma_data_direction dir,

On Wed, Jul 11, 2018 at 10:27:07AM +0800, Tiwei Bie
wrote:
> Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
> ---
>  include/uapi/linux/virtio_config.h |  3 +++
>  include/uapi/linux/virtio_ring.h   | 43 ++++++++++++++++++++++++++++++
>  2 files changed, 46 insertions(+)
> 
> diff --git a/include/uapi/linux/virtio_config.h
b/include/uapi/linux/virtio_config.h
> index 449132c76b1c..1196e1c1d4f6 100644
> --- a/include/uapi/linux/virtio_config.h
> +++ b/include/uapi/linux/virtio_config.h
> @@ -75,6 +75,9 @@
>   */
>  #define VIRTIO_F_IOMMU_PLATFORM		33
>  
> +/* This feature indicates support for the packed virtqueue layout. */
> +#define VIRTIO_F_RING_PACKED		34
> +
>  /*
>   * Does the device support Single Root I/O Virtualization?
>   */
> diff --git a/include/uapi/linux/virtio_ring.h
b/include/uapi/linux/virtio_ring.h
> index 6d5d5faa989b..0254a2ba29cf 100644
> --- a/include/uapi/linux/virtio_ring.h
> +++ b/include/uapi/linux/virtio_ring.h
> @@ -44,6 +44,10 @@
>  /* This means the buffer contains a list of buffer descriptors. */
>  #define VRING_DESC_F_INDIRECT	4
>  
> +/* Mark a descriptor as available or used. */
> +#define VRING_DESC_F_AVAIL	(1ul << 7)
> +#define VRING_DESC_F_USED	(1ul << 15)
> +
>  /* The Host uses this in used->flags to advise the Guest: don't
kick me when
>   * you add a buffer.  It's unreliable, so it's simply an
optimization.  Guest
>   * will still kick if it's out of buffers. */
> @@ -53,6 +57,17 @@
>   * optimization.  */
>  #define VRING_AVAIL_F_NO_INTERRUPT	1
>  
> +/* Enable events. */
> +#define VRING_EVENT_F_ENABLE	0x0
> +/* Disable events. */
> +#define VRING_EVENT_F_DISABLE	0x1
> +/*
> + * Enable events for a specific descriptor
> + * (as specified by Descriptor Ring Change Event Offset/Wrap Counter).
> + * Only valid if VIRTIO_RING_F_EVENT_IDX has been negotiated.
> + */
> +#define VRING_EVENT_F_DESC	0x2
> +
>  /* We support indirect buffer descriptors */
>  #define VIRTIO_RING_F_INDIRECT_DESC	28
>  
These are for the packed ring, right? Pls prefix accordingly.
Also, you likely need macros for the wrap counters.
> @@ -171,4 +186,32 @@ static inline int vring_need_event(__u16 event_idx,
__u16 new_idx, __u16 old)
>  	return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
>  }
>  
> +struct vring_packed_desc_event {
> +	/* Descriptor Ring Change Event Offset/Wrap Counter. */
> +	__virtio16 off_wrap;
> +	/* Descriptor Ring Change Event Flags. */
> +	__virtio16 flags;
> +};
> +
> +struct vring_packed_desc {
> +	/* Buffer Address. */
> +	__virtio64 addr;
> +	/* Buffer Length. */
> +	__virtio32 len;
> +	/* Buffer ID. */
> +	__virtio16 id;
> +	/* The flags depending on descriptor type. */
> +	__virtio16 flags;
> +};
Don't use __virtioXX types, just __leXX ones.
> +
> +struct vring_packed {
> +	unsigned int num;
> +
> +	struct vring_packed_desc *desc;
> +
> +	struct vring_packed_desc_event *driver;
> +
> +	struct vring_packed_desc_event *device;
> +};
> +
>  #endif /* _UAPI_LINUX_VIRTIO_RING_H */
> -- 
> 2.18.0

On Wed, Jul 11, 2018 at 10:27:08AM +0800, Tiwei Bie
wrote:
> This commit introduces the support for creating packed ring.
> All split ring specific functions are added _split suffix.
> Some necessary stubs for packed ring are also added.
> 
> Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
I'd rather have a patch just renaming split functions, then
add all packed stuff in as a separate patch on top.

> ---
>  drivers/virtio/virtio_ring.c | 801 +++++++++++++++++++++++------------
>  include/linux/virtio_ring.h  |   8 +-
>  2 files changed, 546 insertions(+), 263 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 814b395007b2..c4f8abc7445a 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -60,11 +60,15 @@ struct vring_desc_state {
>  	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
>  };
>  
> +struct vring_desc_state_packed {
> +	int next;			/* The next desc state. */
So this can go away with IN_ORDER?
> +};
> +
>  struct vring_virtqueue {
>  	struct virtqueue vq;
>  
> -	/* Actual memory layout for this queue */
> -	struct vring vring;
> +	/* Is this a packed ring? */
> +	bool packed;
>  
>  	/* Can we use weak barriers? */
>  	bool weak_barriers;
> @@ -86,11 +90,39 @@ struct vring_virtqueue {
>  	/* Last used index we've seen. */
>  	u16 last_used_idx;
>  
> -	/* Last written value to avail->flags */
> -	u16 avail_flags_shadow;
> +	union {
> +		/* Available for split ring */
> +		struct {
> +			/* Actual memory layout for this queue. */
> +			struct vring vring;
>  
> -	/* Last written value to avail->idx in guest byte order */
> -	u16 avail_idx_shadow;
> +			/* Last written value to avail->flags */
> +			u16 avail_flags_shadow;
> +
> +			/* Last written value to avail->idx in
> +			 * guest byte order. */
> +			u16 avail_idx_shadow;
> +		};
Name this field split so it's easier to detect misuse of e.g.
packed fields in split code?
> +
> +		/* Available for packed ring */
> +		struct {
> +			/* Actual memory layout for this queue. */
> +			struct vring_packed vring_packed;
> +
> +			/* Driver ring wrap counter. */
> +			bool avail_wrap_counter;
> +
> +			/* Device ring wrap counter. */
> +			bool used_wrap_counter;
> +
> +			/* Index of the next avail descriptor. */
> +			u16 next_avail_idx;
> +
> +			/* Last written value to driver->flags in
> +			 * guest byte order. */
> +			u16 event_flags_shadow;
> +		};
> +	};
>  
>  	/* How to notify other side. FIXME: commonalize hcalls! */
>  	bool (*notify)(struct virtqueue *vq);
> @@ -110,11 +142,24 @@ struct vring_virtqueue {
>  #endif
>  
>  	/* Per-descriptor state. */
> -	struct vring_desc_state desc_state[];
> +	union {
> +		struct vring_desc_state desc_state[1];
> +		struct vring_desc_state_packed desc_state_packed[1];
> +	};
>  };
>  
>  #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
>  
> +static inline bool virtqueue_use_indirect(struct virtqueue *_vq,
> +					  unsigned int total_sg)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	/* If the host supports indirect descriptor tables, and we have multiple
> +	 * buffers, then go indirect. FIXME: tune this threshold */
> +	return (vq->indirect && total_sg > 1 &&
vq->vq.num_free);
> +}
> +
>  /*
>   * Modern virtio devices have feature bits to specify whether they need a
>   * quirk and bypass the IOMMU. If not there, just use the DMA API.
> @@ -200,8 +245,17 @@ static dma_addr_t vring_map_single(const struct
vring_virtqueue *vq,
>  			      cpu_addr, size, direction);
>  }
>  
> -static void vring_unmap_one(const struct vring_virtqueue *vq,
> -			    struct vring_desc *desc)
> +static int vring_mapping_error(const struct vring_virtqueue *vq,
> +			       dma_addr_t addr)
> +{
> +	if (!vring_use_dma_api(vq->vq.vdev))
> +		return 0;
> +
> +	return dma_mapping_error(vring_dma_dev(vq), addr);
> +}
> +
> +static void vring_unmap_one_split(const struct vring_virtqueue *vq,
> +				  struct vring_desc *desc)
>  {
>  	u16 flags;
>  
> @@ -225,17 +279,9 @@ static void vring_unmap_one(const struct
vring_virtqueue *vq,
>  	}
>  }
>  
> -static int vring_mapping_error(const struct vring_virtqueue *vq,
> -			       dma_addr_t addr)
> -{
> -	if (!vring_use_dma_api(vq->vq.vdev))
> -		return 0;
> -
> -	return dma_mapping_error(vring_dma_dev(vq), addr);
> -}
> -
> -static struct vring_desc *alloc_indirect(struct virtqueue *_vq,
> -					 unsigned int total_sg, gfp_t gfp)
> +static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
> +					       unsigned int total_sg,
> +					       gfp_t gfp)
>  {
>  	struct vring_desc *desc;
>  	unsigned int i;
> @@ -256,14 +302,14 @@ static struct vring_desc *alloc_indirect(struct
virtqueue *_vq,
>  	return desc;
>  }
>  
> -static inline int virtqueue_add(struct virtqueue *_vq,
> -				struct scatterlist *sgs[],
> -				unsigned int total_sg,
> -				unsigned int out_sgs,
> -				unsigned int in_sgs,
> -				void *data,
> -				void *ctx,
> -				gfp_t gfp)
> +static inline int virtqueue_add_split(struct virtqueue *_vq,
> +				      struct scatterlist *sgs[],
> +				      unsigned int total_sg,
> +				      unsigned int out_sgs,
> +				      unsigned int in_sgs,
> +				      void *data,
> +				      void *ctx,
> +				      gfp_t gfp)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  	struct scatterlist *sg;
> @@ -299,10 +345,8 @@ static inline int virtqueue_add(struct virtqueue *_vq,
>  
>  	head = vq->free_head;
>  
> -	/* If the host supports indirect descriptor tables, and we have multiple
> -	 * buffers, then go indirect. FIXME: tune this threshold */
> -	if (vq->indirect && total_sg > 1 &&
vq->vq.num_free)
> -		desc = alloc_indirect(_vq, total_sg, gfp);
> +	if (virtqueue_use_indirect(_vq, total_sg))
> +		desc = alloc_indirect_split(_vq, total_sg, gfp);
>  	else {
>  		desc = NULL;
>  		WARN_ON_ONCE(total_sg > vq->vring.num &&
!vq->indirect);
> @@ -423,7 +467,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
>  	for (n = 0; n < total_sg; n++) {
>  		if (i == err_idx)
>  			break;
> -		vring_unmap_one(vq, &desc[i]);
> +		vring_unmap_one_split(vq, &desc[i]);
>  		i = virtio16_to_cpu(_vq->vdev, vq->vring.desc[i].next);
>  	}
>  
> @@ -434,6 +478,355 @@ static inline int virtqueue_add(struct virtqueue
*_vq,
>  	return -EIO;
>  }
>  
> +static bool virtqueue_kick_prepare_split(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 new, old;
> +	bool needs_kick;
> +
> +	START_USE(vq);
> +	/* We need to expose available array entries before checking avail
> +	 * event. */
> +	virtio_mb(vq->weak_barriers);
> +
> +	old = vq->avail_idx_shadow - vq->num_added;
> +	new = vq->avail_idx_shadow;
> +	vq->num_added = 0;
> +
> +#ifdef DEBUG
> +	if (vq->last_add_time_valid) {
> +		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
> +					      vq->last_add_time)) > 100);
> +	}
> +	vq->last_add_time_valid = false;
> +#endif
> +
> +	if (vq->event) {
> +		needs_kick = vring_need_event(virtio16_to_cpu(_vq->vdev,
vring_avail_event(&vq->vring)),
> +					      new, old);
> +	} else {
> +		needs_kick = !(vq->vring.used->flags &
cpu_to_virtio16(_vq->vdev, VRING_USED_F_NO_NOTIFY));
> +	}
> +	END_USE(vq);
> +	return needs_kick;
> +}
> +
> +static void detach_buf_split(struct vring_virtqueue *vq, unsigned int
head,
> +			     void **ctx)
> +{
> +	unsigned int i, j;
> +	__virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
> +
> +	/* Clear data ptr. */
> +	vq->desc_state[head].data = NULL;
> +
> +	/* Put back on free list: unmap first-level descriptors and find end */
> +	i = head;
> +
> +	while (vq->vring.desc[i].flags & nextflag) {
> +		vring_unmap_one_split(vq, &vq->vring.desc[i]);
> +		i = virtio16_to_cpu(vq->vq.vdev, vq->vring.desc[i].next);
> +		vq->vq.num_free++;
> +	}
> +
> +	vring_unmap_one_split(vq, &vq->vring.desc[i]);
> +	vq->vring.desc[i].next = cpu_to_virtio16(vq->vq.vdev,
vq->free_head);
> +	vq->free_head = head;
> +
> +	/* Plus final descriptor */
> +	vq->vq.num_free++;
> +
> +	if (vq->indirect) {
> +		struct vring_desc *indir_desc = vq->desc_state[head].indir_desc;
> +		u32 len;
> +
> +		/* Free the indirect table, if any, now that it's unmapped. */
> +		if (!indir_desc)
> +			return;
> +
> +		len = virtio32_to_cpu(vq->vq.vdev, vq->vring.desc[head].len);
> +
> +		BUG_ON(!(vq->vring.desc[head].flags &
> +			 cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT)));
> +		BUG_ON(len == 0 || len % sizeof(struct vring_desc));
> +
> +		for (j = 0; j < len / sizeof(struct vring_desc); j++)
> +			vring_unmap_one_split(vq, &indir_desc[j]);
> +
> +		kfree(indir_desc);
> +		vq->desc_state[head].indir_desc = NULL;
> +	} else if (ctx) {
> +		*ctx = vq->desc_state[head].indir_desc;
> +	}
> +}
> +
> +static inline bool more_used_split(const struct vring_virtqueue *vq)
> +{
> +	return vq->last_used_idx != virtio16_to_cpu(vq->vq.vdev,
vq->vring.used->idx);
> +}
> +
> +static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq,
> +					 unsigned int *len,
> +					 void **ctx)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	void *ret;
> +	unsigned int i;
> +	u16 last_used;
> +
> +	START_USE(vq);
> +
> +	if (unlikely(vq->broken)) {
> +		END_USE(vq);
> +		return NULL;
> +	}
> +
> +	if (!more_used_split(vq)) {
> +		pr_debug("No more buffers in queue\n");
> +		END_USE(vq);
> +		return NULL;
> +	}
> +
> +	/* Only get used array entries after they have been exposed by host. */
> +	virtio_rmb(vq->weak_barriers);
> +
> +	last_used = (vq->last_used_idx & (vq->vring.num - 1));
> +	i = virtio32_to_cpu(_vq->vdev,
vq->vring.used->ring[last_used].id);
> +	*len = virtio32_to_cpu(_vq->vdev,
vq->vring.used->ring[last_used].len);
> +
> +	if (unlikely(i >= vq->vring.num)) {
> +		BAD_RING(vq, "id %u out of range\n", i);
> +		return NULL;
> +	}
> +	if (unlikely(!vq->desc_state[i].data)) {
> +		BAD_RING(vq, "id %u is not a head!\n", i);
> +		return NULL;
> +	}
> +
> +	/* detach_buf_split clears data, so grab it now. */
> +	ret = vq->desc_state[i].data;
> +	detach_buf_split(vq, i, ctx);
> +	vq->last_used_idx++;
> +	/* If we expect an interrupt for the next entry, tell host
> +	 * by writing event index and flush out the write before
> +	 * the read in the next get_buf call. */
> +	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
> +		virtio_store_mb(vq->weak_barriers,
> +				&vring_used_event(&vq->vring),
> +				cpu_to_virtio16(_vq->vdev, vq->last_used_idx));
> +
> +#ifdef DEBUG
> +	vq->last_add_time_valid = false;
> +#endif
> +
> +	END_USE(vq);
> +	return ret;
> +}
> +
> +static void virtqueue_disable_cb_split(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {
> +		vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
> +		if (!vq->event)
> +			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
> +	}
> +}
> +
> +static unsigned virtqueue_enable_cb_prepare_split(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 last_used_idx;
> +
> +	START_USE(vq);
> +
> +	/* We optimistically turn back on interrupts, then check if there was
> +	 * more to do. */
> +	/* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
> +	 * either clear the flags bit or point the event index at the next
> +	 * entry. Always do both to keep code simple. */
> +	if (vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) {
> +		vq->avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT;
> +		if (!vq->event)
> +			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
> +	}
> +	vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev,
last_used_idx = vq->last_used_idx);
> +	END_USE(vq);
> +	return last_used_idx;
> +}
> +
> +static bool virtqueue_poll_split(struct virtqueue *_vq, unsigned
last_used_idx)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	virtio_mb(vq->weak_barriers);
> +	return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev,
vq->vring.used->idx);
> +}
> +
> +static bool virtqueue_enable_cb_delayed_split(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 bufs;
> +
> +	START_USE(vq);
> +
> +	/* We optimistically turn back on interrupts, then check if there was
> +	 * more to do. */
> +	/* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
> +	 * either clear the flags bit or point the event index at the next
> +	 * entry. Always update the event index to keep code simple. */
> +	if (vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) {
> +		vq->avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT;
> +		if (!vq->event)
> +			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
> +	}
> +	/* TODO: tune this threshold */
> +	bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4;
> +
> +	virtio_store_mb(vq->weak_barriers,
> +			&vring_used_event(&vq->vring),
> +			cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs));
> +
> +	if (unlikely((u16)(virtio16_to_cpu(_vq->vdev,
vq->vring.used->idx) - vq->last_used_idx) > bufs)) {
> +		END_USE(vq);
> +		return false;
> +	}
> +
> +	END_USE(vq);
> +	return true;
> +}
> +
> +static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	unsigned int i;
> +	void *buf;
> +
> +	START_USE(vq);
> +
> +	for (i = 0; i < vq->vring.num; i++) {
> +		if (!vq->desc_state[i].data)
> +			continue;
> +		/* detach_buf clears data, so grab it now. */
> +		buf = vq->desc_state[i].data;
> +		detach_buf_split(vq, i, NULL);
> +		vq->avail_idx_shadow--;
> +		vq->vring.avail->idx = cpu_to_virtio16(_vq->vdev,
vq->avail_idx_shadow);
> +		END_USE(vq);
> +		return buf;
> +	}
> +	/* That should have freed everything. */
> +	BUG_ON(vq->vq.num_free != vq->vring.num);
> +
> +	END_USE(vq);
> +	return NULL;
> +}
> +
> +/*
> + * The layout for the packed ring is a continuous chunk of memory
> + * which looks like this.
> + *
> + * struct vring_packed {
> + *	// The actual descriptors (16 bytes each)
> + *	struct vring_packed_desc desc[num];
> + *
> + *	// Padding to the next align boundary.
> + *	char pad[];
> + *
> + *	// Driver Event Suppression
> + *	struct vring_packed_desc_event driver;
> + *
> + *	// Device Event Suppression
> + *	struct vring_packed_desc_event device;
> + * };
> + */
Why not just allocate event structures separately?
Is it a win to have them share a cache line for some reason?
> +static inline void vring_init_packed(struct vring_packed *vr, unsigned int
num,
> +				     void *p, unsigned long align)
> +{
> +	vr->num = num;
> +	vr->desc = p;
> +	vr->driver = (void *)ALIGN(((uintptr_t)p +
> +		sizeof(struct vring_packed_desc) * num), align);
> +	vr->device = vr->driver + 1;
> +}
What's all this about alignment? Where does it come from?
> +
> +static inline unsigned vring_size_packed(unsigned int num, unsigned long
align)
> +{
> +	return ((sizeof(struct vring_packed_desc) * num + align - 1)
> +		& ~(align - 1)) + sizeof(struct vring_packed_desc_event) * 2;
> +}
> +
> +static inline int virtqueue_add_packed(struct virtqueue *_vq,
> +				       struct scatterlist *sgs[],
> +				       unsigned int total_sg,
> +				       unsigned int out_sgs,
> +				       unsigned int in_sgs,
> +				       void *data,
> +				       void *ctx,
> +				       gfp_t gfp)
> +{
> +	return -EIO;
> +}
> +
> +static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
> +{
> +	return false;
> +}
> +
> +static inline bool more_used_packed(const struct vring_virtqueue *vq)
> +{
> +	return false;
> +}
> +
> +static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
> +					  unsigned int *len,
> +					  void **ctx)
> +{
> +	return NULL;
> +}
> +
> +static void virtqueue_disable_cb_packed(struct virtqueue *_vq)
> +{
> +}
> +
> +static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq)
> +{
> +	return 0;
> +}
> +
> +static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned
last_used_idx)
> +{
> +	return false;
> +}
> +
> +static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
> +{
> +	return false;
> +}
> +
> +static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
> +{
> +	return NULL;
> +}
> +
> +static inline int virtqueue_add(struct virtqueue *_vq,
> +				struct scatterlist *sgs[],
> +				unsigned int total_sg,
> +				unsigned int out_sgs,
> +				unsigned int in_sgs,
> +				void *data,
> +				void *ctx,
> +				gfp_t gfp)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	return vq->packed ? virtqueue_add_packed(_vq, sgs, total_sg, out_sgs,
> +						 in_sgs, data, ctx, gfp) :
> +			    virtqueue_add_split(_vq, sgs, total_sg, out_sgs,
> +						in_sgs, data, ctx, gfp);
> +}
> +
>  /**
>   * virtqueue_add_sgs - expose buffers to other end
>   * @vq: the struct virtqueue we're talking about.
> @@ -550,34 +943,9 @@ EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_ctx);
>  bool virtqueue_kick_prepare(struct virtqueue *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
> -	u16 new, old;
> -	bool needs_kick;
>  
> -	START_USE(vq);
> -	/* We need to expose available array entries before checking avail
> -	 * event. */
> -	virtio_mb(vq->weak_barriers);
> -
> -	old = vq->avail_idx_shadow - vq->num_added;
> -	new = vq->avail_idx_shadow;
> -	vq->num_added = 0;
> -
> -#ifdef DEBUG
> -	if (vq->last_add_time_valid) {
> -		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
> -					      vq->last_add_time)) > 100);
> -	}
> -	vq->last_add_time_valid = false;
> -#endif
> -
> -	if (vq->event) {
> -		needs_kick = vring_need_event(virtio16_to_cpu(_vq->vdev,
vring_avail_event(&vq->vring)),
> -					      new, old);
> -	} else {
> -		needs_kick = !(vq->vring.used->flags &
cpu_to_virtio16(_vq->vdev, VRING_USED_F_NO_NOTIFY));
> -	}
> -	END_USE(vq);
> -	return needs_kick;
> +	return vq->packed ? virtqueue_kick_prepare_packed(_vq) :
> +			    virtqueue_kick_prepare_split(_vq);
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);
>  
> @@ -625,58 +993,9 @@ bool virtqueue_kick(struct virtqueue *vq)
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_kick);
>  
> -static void detach_buf(struct vring_virtqueue *vq, unsigned int head,
> -		       void **ctx)
> -{
> -	unsigned int i, j;
> -	__virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
> -
> -	/* Clear data ptr. */
> -	vq->desc_state[head].data = NULL;
> -
> -	/* Put back on free list: unmap first-level descriptors and find end */
> -	i = head;
> -
> -	while (vq->vring.desc[i].flags & nextflag) {
> -		vring_unmap_one(vq, &vq->vring.desc[i]);
> -		i = virtio16_to_cpu(vq->vq.vdev, vq->vring.desc[i].next);
> -		vq->vq.num_free++;
> -	}
> -
> -	vring_unmap_one(vq, &vq->vring.desc[i]);
> -	vq->vring.desc[i].next = cpu_to_virtio16(vq->vq.vdev,
vq->free_head);
> -	vq->free_head = head;
> -
> -	/* Plus final descriptor */
> -	vq->vq.num_free++;
> -
> -	if (vq->indirect) {
> -		struct vring_desc *indir_desc = vq->desc_state[head].indir_desc;
> -		u32 len;
> -
> -		/* Free the indirect table, if any, now that it's unmapped. */
> -		if (!indir_desc)
> -			return;
> -
> -		len = virtio32_to_cpu(vq->vq.vdev, vq->vring.desc[head].len);
> -
> -		BUG_ON(!(vq->vring.desc[head].flags &
> -			 cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT)));
> -		BUG_ON(len == 0 || len % sizeof(struct vring_desc));
> -
> -		for (j = 0; j < len / sizeof(struct vring_desc); j++)
> -			vring_unmap_one(vq, &indir_desc[j]);
> -
> -		kfree(indir_desc);
> -		vq->desc_state[head].indir_desc = NULL;
> -	} else if (ctx) {
> -		*ctx = vq->desc_state[head].indir_desc;
> -	}
> -}
> -
>  static inline bool more_used(const struct vring_virtqueue *vq)
>  {
> -	return vq->last_used_idx != virtio16_to_cpu(vq->vq.vdev,
vq->vring.used->idx);
> +	return vq->packed ? more_used_packed(vq) : more_used_split(vq);
>  }
>  
>  /**
> @@ -699,57 +1018,9 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq,
unsigned int *len,
>  			    void **ctx)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
> -	void *ret;
> -	unsigned int i;
> -	u16 last_used;
>  
> -	START_USE(vq);
> -
> -	if (unlikely(vq->broken)) {
> -		END_USE(vq);
> -		return NULL;
> -	}
> -
> -	if (!more_used(vq)) {
> -		pr_debug("No more buffers in queue\n");
> -		END_USE(vq);
> -		return NULL;
> -	}
> -
> -	/* Only get used array entries after they have been exposed by host. */
> -	virtio_rmb(vq->weak_barriers);
> -
> -	last_used = (vq->last_used_idx & (vq->vring.num - 1));
> -	i = virtio32_to_cpu(_vq->vdev,
vq->vring.used->ring[last_used].id);
> -	*len = virtio32_to_cpu(_vq->vdev,
vq->vring.used->ring[last_used].len);
> -
> -	if (unlikely(i >= vq->vring.num)) {
> -		BAD_RING(vq, "id %u out of range\n", i);
> -		return NULL;
> -	}
> -	if (unlikely(!vq->desc_state[i].data)) {
> -		BAD_RING(vq, "id %u is not a head!\n", i);
> -		return NULL;
> -	}
> -
> -	/* detach_buf clears data, so grab it now. */
> -	ret = vq->desc_state[i].data;
> -	detach_buf(vq, i, ctx);
> -	vq->last_used_idx++;
> -	/* If we expect an interrupt for the next entry, tell host
> -	 * by writing event index and flush out the write before
> -	 * the read in the next get_buf call. */
> -	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
> -		virtio_store_mb(vq->weak_barriers,
> -				&vring_used_event(&vq->vring),
> -				cpu_to_virtio16(_vq->vdev, vq->last_used_idx));
> -
> -#ifdef DEBUG
> -	vq->last_add_time_valid = false;
> -#endif
> -
> -	END_USE(vq);
> -	return ret;
> +	return vq->packed ? virtqueue_get_buf_ctx_packed(_vq, len, ctx) :
> +			    virtqueue_get_buf_ctx_split(_vq, len, ctx);
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_get_buf_ctx);
>  
> @@ -771,12 +1042,10 @@ void virtqueue_disable_cb(struct virtqueue *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  
> -	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {
> -		vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
> -		if (!vq->event)
> -			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
> -	}
> -
> +	if (vq->packed)
> +		virtqueue_disable_cb_packed(_vq);
> +	else
> +		virtqueue_disable_cb_split(_vq);
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
>  
> @@ -795,23 +1064,9 @@ EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
>  unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
> -	u16 last_used_idx;
>  
> -	START_USE(vq);
> -
> -	/* We optimistically turn back on interrupts, then check if there was
> -	 * more to do. */
> -	/* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
> -	 * either clear the flags bit or point the event index at the next
> -	 * entry. Always do both to keep code simple. */
> -	if (vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) {
> -		vq->avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT;
> -		if (!vq->event)
> -			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
> -	}
> -	vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev,
last_used_idx = vq->last_used_idx);
> -	END_USE(vq);
> -	return last_used_idx;
> +	return vq->packed ? virtqueue_enable_cb_prepare_packed(_vq) :
> +			    virtqueue_enable_cb_prepare_split(_vq);
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);
>  
> @@ -828,8 +1083,8 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned
last_used_idx)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  
> -	virtio_mb(vq->weak_barriers);
> -	return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev,
vq->vring.used->idx);
> +	return vq->packed ? virtqueue_poll_packed(_vq, last_used_idx) :
> +			    virtqueue_poll_split(_vq, last_used_idx);
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_poll);
>  
> @@ -867,34 +1122,9 @@ EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
>  bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
> -	u16 bufs;
>  
> -	START_USE(vq);
> -
> -	/* We optimistically turn back on interrupts, then check if there was
> -	 * more to do. */
> -	/* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
> -	 * either clear the flags bit or point the event index at the next
> -	 * entry. Always update the event index to keep code simple. */
> -	if (vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) {
> -		vq->avail_flags_shadow &= ~VRING_AVAIL_F_NO_INTERRUPT;
> -		if (!vq->event)
> -			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
vq->avail_flags_shadow);
> -	}
> -	/* TODO: tune this threshold */
> -	bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4;
> -
> -	virtio_store_mb(vq->weak_barriers,
> -			&vring_used_event(&vq->vring),
> -			cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs));
> -
> -	if (unlikely((u16)(virtio16_to_cpu(_vq->vdev,
vq->vring.used->idx) - vq->last_used_idx) > bufs)) {
> -		END_USE(vq);
> -		return false;
> -	}
> -
> -	END_USE(vq);
> -	return true;
> +	return vq->packed ? virtqueue_enable_cb_delayed_packed(_vq) :
> +			    virtqueue_enable_cb_delayed_split(_vq);
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
>  
> @@ -909,27 +1139,9 @@ EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
>  void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
> -	unsigned int i;
> -	void *buf;
>  
> -	START_USE(vq);
> -
> -	for (i = 0; i < vq->vring.num; i++) {
> -		if (!vq->desc_state[i].data)
> -			continue;
> -		/* detach_buf clears data, so grab it now. */
> -		buf = vq->desc_state[i].data;
> -		detach_buf(vq, i, NULL);
> -		vq->avail_idx_shadow--;
> -		vq->vring.avail->idx = cpu_to_virtio16(_vq->vdev,
vq->avail_idx_shadow);
> -		END_USE(vq);
> -		return buf;
> -	}
> -	/* That should have freed everything. */
> -	BUG_ON(vq->vq.num_free != vq->vring.num);
> -
> -	END_USE(vq);
> -	return NULL;
> +	return vq->packed ? virtqueue_detach_unused_buf_packed(_vq) :
> +			    virtqueue_detach_unused_buf_split(_vq);
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
>  
> @@ -954,7 +1166,8 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
>  EXPORT_SYMBOL_GPL(vring_interrupt);
>  
>  struct virtqueue *__vring_new_virtqueue(unsigned int index,
> -					struct vring vring,
> +					union vring_union vring,
> +					bool packed,
>  					struct virtio_device *vdev,
>  					bool weak_barriers,
>  					bool context,
> @@ -962,19 +1175,22 @@ struct virtqueue *__vring_new_virtqueue(unsigned int
index,
>  					void (*callback)(struct virtqueue *),
>  					const char *name)
>  {
> -	unsigned int i;
>  	struct vring_virtqueue *vq;
> +	unsigned int num, i;
> +	size_t size;
>  
> -	vq = kmalloc(sizeof(*vq) + vring.num * sizeof(struct vring_desc_state),
> -		     GFP_KERNEL);
> +	num = packed ? vring.vring_packed.num : vring.vring_split.num;
> +	size = packed ? num * sizeof(struct vring_desc_state_packed) :
> +			num * sizeof(struct vring_desc_state);
> +
> +	vq = kmalloc(sizeof(*vq) + size, GFP_KERNEL);
>  	if (!vq)
>  		return NULL;
>  
> -	vq->vring = vring;
>  	vq->vq.callback = callback;
>  	vq->vq.vdev = vdev;
>  	vq->vq.name = name;
> -	vq->vq.num_free = vring.num;
> +	vq->vq.num_free = num;
>  	vq->vq.index = index;
>  	vq->we_own_ring = false;
>  	vq->queue_dma_addr = 0;
> @@ -983,9 +1199,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int
index,
>  	vq->weak_barriers = weak_barriers;
>  	vq->broken = false;
>  	vq->last_used_idx = 0;
> -	vq->avail_flags_shadow = 0;
> -	vq->avail_idx_shadow = 0;
>  	vq->num_added = 0;
> +	vq->packed = packed;
>  	list_add_tail(&vq->vq.list, &vdev->vqs);
>  #ifdef DEBUG
>  	vq->in_use = false;
> @@ -996,19 +1211,48 @@ struct virtqueue *__vring_new_virtqueue(unsigned int
index,
>  		!context;
>  	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
>  
> +	if (vq->packed) {
> +		vq->vring_packed = vring.vring_packed;
> +		vq->next_avail_idx = 0;
> +		vq->avail_wrap_counter = 1;
> +		vq->used_wrap_counter = 1;
> +		vq->event_flags_shadow = 0;
> +
> +		memset(vq->desc_state_packed, 0,
> +			num * sizeof(struct vring_desc_state_packed));
> +
> +		/* Put everything in free lists. */
> +		vq->free_head = 0;
> +		for (i = 0; i < num-1; i++)
> +			vq->desc_state_packed[i].next = i + 1;
> +	} else {
> +		vq->vring = vring.vring_split;
> +		vq->avail_flags_shadow = 0;
> +		vq->avail_idx_shadow = 0;
> +
> +		/* Put everything in free lists. */
> +		vq->free_head = 0;
> +		for (i = 0; i < num-1; i++)
> +			vq->vring.desc[i].next = cpu_to_virtio16(vdev, i + 1);
> +
> +		memset(vq->desc_state, 0,
> +			num * sizeof(struct vring_desc_state));
> +	}
> +
>  	/* No callback?  Tell other side not to bother us. */
>  	if (!callback) {
> -		vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
> -		if (!vq->event)
> -			vq->vring.avail->flags = cpu_to_virtio16(vdev,
vq->avail_flags_shadow);
> +		if (packed) {
> +			vq->event_flags_shadow = VRING_EVENT_F_DISABLE;
> +			vq->vring_packed.driver->flags = cpu_to_virtio16(vdev,
> +						vq->event_flags_shadow);
> +		} else {
> +			vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
> +			if (!vq->event)
> +				vq->vring.avail->flags = cpu_to_virtio16(vdev,
> +						vq->avail_flags_shadow);
> +		}
>  	}
>  
> -	/* Put everything in free lists. */
> -	vq->free_head = 0;
> -	for (i = 0; i < vring.num-1; i++)
> -		vq->vring.desc[i].next = cpu_to_virtio16(vdev, i + 1);
> -	memset(vq->desc_state, 0, vring.num * sizeof(struct
vring_desc_state));
> -
>  	return &vq->vq;
>  }
>  EXPORT_SYMBOL_GPL(__vring_new_virtqueue);
> @@ -1055,6 +1299,12 @@ static void vring_free_queue(struct virtio_device
*vdev, size_t size,
>  	}
>  }
>  
> +static inline int
> +__vring_size(unsigned int num, unsigned long align, bool packed)
> +{
> +	return packed ? vring_size_packed(num, align) : vring_size(num, align);
> +}
> +
>  struct virtqueue *vring_create_virtqueue(
>  	unsigned int index,
>  	unsigned int num,
> @@ -1071,7 +1321,8 @@ struct virtqueue *vring_create_virtqueue(
>  	void *queue = NULL;
>  	dma_addr_t dma_addr;
>  	size_t queue_size_in_bytes;
> -	struct vring vring;
> +	union vring_union vring;
> +	bool packed;
>  
>  	/* We assume num is a power of 2. */
>  	if (num & (num - 1)) {
> @@ -1079,9 +1330,13 @@ struct virtqueue *vring_create_virtqueue(
>  		return NULL;
>  	}
>  
> +	packed = virtio_has_feature(vdev, VIRTIO_F_RING_PACKED);
> +
>  	/* TODO: allocate each queue chunk individually */
> -	for (; num && vring_size(num, vring_align) > PAGE_SIZE; num /=
2) {
> -		queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
> +	for (; num && __vring_size(num, vring_align, packed) >
PAGE_SIZE;
> +			num /= 2) {
> +		queue = vring_alloc_queue(vdev, __vring_size(num, vring_align,
> +							     packed),
>  					  &dma_addr,
>  					  GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
>  		if (queue)
> @@ -1093,17 +1348,21 @@ struct virtqueue *vring_create_virtqueue(
>  
>  	if (!queue) {
>  		/* Try to get a single page. You are my only hope! */
> -		queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
> +		queue = vring_alloc_queue(vdev, __vring_size(num, vring_align,
> +							     packed),
>  					  &dma_addr, GFP_KERNEL|__GFP_ZERO);
>  	}
>  	if (!queue)
>  		return NULL;
>  
> -	queue_size_in_bytes = vring_size(num, vring_align);
> -	vring_init(&vring, num, queue, vring_align);
> +	queue_size_in_bytes = __vring_size(num, vring_align, packed);
> +	if (packed)
> +		vring_init_packed(&vring.vring_packed, num, queue, vring_align);
> +	else
> +		vring_init(&vring.vring_split, num, queue, vring_align);
>  
> -	vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
> -				   notify, callback, name);
> +	vq = __vring_new_virtqueue(index, vring, packed, vdev, weak_barriers,
> +				   context, notify, callback, name);
>  	if (!vq) {
>  		vring_free_queue(vdev, queue_size_in_bytes, queue,
>  				 dma_addr);
> @@ -1129,10 +1388,17 @@ struct virtqueue *vring_new_virtqueue(unsigned int
index,
>  				      void (*callback)(struct virtqueue *vq),
>  				      const char *name)
>  {
> -	struct vring vring;
> -	vring_init(&vring, num, pages, vring_align);
> -	return __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
> -				     notify, callback, name);
> +	union vring_union vring;
> +	bool packed;
> +
> +	packed = virtio_has_feature(vdev, VIRTIO_F_RING_PACKED);
> +	if (packed)
> +		vring_init_packed(&vring.vring_packed, num, pages, vring_align);
> +	else
> +		vring_init(&vring.vring_split, num, pages, vring_align);

vring_init in the UAPI header is more or less a bug.
I'd just stop using it, keep it around for legacy userspace.
> +
> +	return __vring_new_virtqueue(index, vring, packed, vdev, weak_barriers,
> +				     context, notify, callback, name);
>  }
>  EXPORT_SYMBOL_GPL(vring_new_virtqueue);
>  
> @@ -1142,7 +1408,9 @@ void vring_del_virtqueue(struct virtqueue *_vq)
>  
>  	if (vq->we_own_ring) {
>  		vring_free_queue(vq->vq.vdev, vq->queue_size_in_bytes,
> -				 vq->vring.desc, vq->queue_dma_addr);
> +				 vq->packed ? (void *)vq->vring_packed.desc :
> +					      (void *)vq->vring.desc,
> +				 vq->queue_dma_addr);
>  	}
>  	list_del(&_vq->list);
>  	kfree(vq);
> @@ -1184,7 +1452,7 @@ unsigned int virtqueue_get_vring_size(struct
virtqueue *_vq)
>  
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  
> -	return vq->vring.num;
> +	return vq->packed ? vq->vring_packed.num : vq->vring.num;
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_get_vring_size);
>  
> @@ -1227,6 +1495,10 @@ dma_addr_t virtqueue_get_avail_addr(struct virtqueue
*_vq)
>  
>  	BUG_ON(!vq->we_own_ring);
>  
> +	if (vq->packed)
> +		return vq->queue_dma_addr + ((char *)vq->vring_packed.driver -
> +				(char *)vq->vring_packed.desc);
> +
>  	return vq->queue_dma_addr +
>  		((char *)vq->vring.avail - (char *)vq->vring.desc);
>  }
> @@ -1238,11 +1510,16 @@ dma_addr_t virtqueue_get_used_addr(struct virtqueue
*_vq)
>  
>  	BUG_ON(!vq->we_own_ring);
>  
> +	if (vq->packed)
> +		return vq->queue_dma_addr + ((char *)vq->vring_packed.device -
> +				(char *)vq->vring_packed.desc);
> +
>  	return vq->queue_dma_addr +
>  		((char *)vq->vring.used - (char *)vq->vring.desc);
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_get_used_addr);
>  
> +/* Only available for split ring */
>  const struct vring *virtqueue_get_vring(struct virtqueue *vq)
>  {
>  	return &to_vvq(vq)->vring;
> diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
> index fab02133a919..992142b35f55 100644
> --- a/include/linux/virtio_ring.h
> +++ b/include/linux/virtio_ring.h
> @@ -60,6 +60,11 @@ static inline void virtio_store_mb(bool weak_barriers,
>  struct virtio_device;
>  struct virtqueue;
>  
> +union vring_union {
> +	struct vring vring_split;
> +	struct vring_packed vring_packed;
> +};
> +
>  /*
>   * Creates a virtqueue and allocates the descriptor ring.  If
>   * may_reduce_num is set, then this may allocate a smaller ring than
> @@ -79,7 +84,8 @@ struct virtqueue *vring_create_virtqueue(unsigned int
index,
>  
>  /* Creates a virtqueue with a custom layout. */
>  struct virtqueue *__vring_new_virtqueue(unsigned int index,
> -					struct vring vring,
> +					union vring_union vring,
> +					bool packed,
>  					struct virtio_device *vdev,
>  					bool weak_barriers,
>  					bool ctx,
> -- 
> 2.18.0

On Wed, Jul 11, 2018 at 10:27:10AM +0800, Tiwei Bie
wrote:
> This commit introduces the EVENT_IDX support in packed ring.
> 
> Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
Besides the usual comment about hard-coded constants like <<15:
does this actually do any good for performance? We don't
have to if we do not want to.
> ---
>  drivers/virtio/virtio_ring.c | 73 ++++++++++++++++++++++++++++++++----
>  1 file changed, 65 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index f317b485ba54..f79a1e17f7d1 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -1050,7 +1050,7 @@ static inline int virtqueue_add_packed(struct
virtqueue *_vq,
>  static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
> -	u16 flags;
> +	u16 new, old, off_wrap, flags, wrap_counter, event_idx;
>  	bool needs_kick;
>  	u32 snapshot;
>  
> @@ -1059,9 +1059,19 @@ static bool virtqueue_kick_prepare_packed(struct
virtqueue *_vq)
>  	 * suppressions. */
>  	virtio_mb(vq->weak_barriers);
>  
> +	old = vq->next_avail_idx - vq->num_added;
> +	new = vq->next_avail_idx;
> +	vq->num_added = 0;
> +
>  	snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device);
> +	off_wrap = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot &
0xffff));
>  	flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16))
& 0x3;

some kind of struct union would be helpful to make this readable.
>  
> +	wrap_counter = off_wrap >> 15;
> +	event_idx = off_wrap & ~(1 << 15);
> +	if (wrap_counter != vq->avail_wrap_counter)
> +		event_idx -= vq->vring_packed.num;
> +
>  #ifdef DEBUG
>  	if (vq->last_add_time_valid) {
>  		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
> @@ -1070,7 +1080,10 @@ static bool virtqueue_kick_prepare_packed(struct
virtqueue *_vq)
>  	vq->last_add_time_valid = false;
>  #endif
>  
> -	needs_kick = (flags != VRING_EVENT_F_DISABLE);
> +	if (flags == VRING_EVENT_F_DESC)
> +		needs_kick = vring_need_event(event_idx, new, old);
> +	else
> +		needs_kick = (flags != VRING_EVENT_F_DISABLE);
>  	END_USE(vq);
>  	return needs_kick;
>  }
> @@ -1185,6 +1198,15 @@ static void *virtqueue_get_buf_ctx_packed(struct
virtqueue *_vq,
>  	ret = vq->desc_state_packed[id].data;
>  	detach_buf_packed(vq, id, ctx);
>  
> +	/* If we expect an interrupt for the next entry, tell host
> +	 * by writing event index and flush out the write before
> +	 * the read in the next get_buf call. */
> +	if (vq->event_flags_shadow == VRING_EVENT_F_DESC)
> +		virtio_store_mb(vq->weak_barriers,
> +				&vq->vring_packed.driver->off_wrap,
> +				cpu_to_virtio16(_vq->vdev, vq->last_used_idx |
> +					((u16)vq->used_wrap_counter << 15)));
> +
>  #ifdef DEBUG
>  	vq->last_add_time_valid = false;
>  #endif
> @@ -1213,8 +1235,18 @@ static unsigned
virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq)
>  	/* We optimistically turn back on interrupts, then check if there was
>  	 * more to do. */
>  
> +	if (vq->event) {
> +		vq->vring_packed.driver->off_wrap = cpu_to_virtio16(_vq->vdev,
> +				vq->last_used_idx |
> +				((u16)vq->used_wrap_counter << 15));
> +		/* We need to update event offset and event wrap
> +		 * counter first before updating event flags. */
> +		virtio_wmb(vq->weak_barriers);
> +	}
> +
>  	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
> -		vq->event_flags_shadow = VRING_EVENT_F_ENABLE;
> +		vq->event_flags_shadow = vq->event ? VRING_EVENT_F_DESC :
> +						     VRING_EVENT_F_ENABLE;
>  		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
>  							vq->event_flags_shadow);
>  	}
> @@ -1238,22 +1270,47 @@ static bool virtqueue_poll_packed(struct virtqueue
*_vq, unsigned off_wrap)
>  static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 bufs, used_idx, wrap_counter;
>  
>  	START_USE(vq);
>  
>  	/* We optimistically turn back on interrupts, then check if there was
>  	 * more to do. */
>  
> +	if (vq->event) {
> +		/* TODO: tune this threshold */
> +		bufs = (vq->vring_packed.num - _vq->num_free) * 3 / 4;
> +		wrap_counter = vq->used_wrap_counter;
> +
> +		used_idx = vq->last_used_idx + bufs;
> +		if (used_idx >= vq->vring_packed.num) {
> +			used_idx -= vq->vring_packed.num;
> +			wrap_counter ^= 1;
> +		}
> +
> +		vq->vring_packed.driver->off_wrap = cpu_to_virtio16(_vq->vdev,
> +				used_idx | (wrap_counter << 15));
> +
> +		/* We need to update event offset and event wrap
> +		 * counter first before updating event flags. */
> +		virtio_wmb(vq->weak_barriers);
> +	} else {
> +		used_idx = vq->last_used_idx;
> +		wrap_counter = vq->used_wrap_counter;
> +	}
> +
>  	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
> -		vq->event_flags_shadow = VRING_EVENT_F_ENABLE;
> +		vq->event_flags_shadow = vq->event ? VRING_EVENT_F_DESC :
> +						     VRING_EVENT_F_ENABLE;
>  		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
>  							vq->event_flags_shadow);
> -		/* We need to enable interrupts first before re-checking
> -		 * for more used buffers. */
> -		virtio_mb(vq->weak_barriers);
>  	}
>  
> -	if (more_used_packed(vq)) {
> +	/* We need to update event suppression structure first
> +	 * before re-checking for more used buffers. */
> +	virtio_mb(vq->weak_barriers);
> +
mb is expensive. We should not do it if we changed nothing.
> +	if (is_used_desc_packed(vq, used_idx, wrap_counter)) {
>  		END_USE(vq);
>  		return false;
>  	}
> -- 
> 2.18.0

On Wed, Jul 11, 2018 at 10:27:09AM +0800, Tiwei Bie
wrote:
> This commit introduces the support (without EVENT_IDX) for
> packed ring.
> 
> Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
> ---
>  drivers/virtio/virtio_ring.c | 495 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 487 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c4f8abc7445a..f317b485ba54 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -55,12 +55,21 @@
>  #define END_USE(vq)
>  #endif
>  
> +#define _VRING_DESC_F_AVAIL(b)	((__u16)(b) << 7)
> +#define _VRING_DESC_F_USED(b)	((__u16)(b) << 15)
> +
>  struct vring_desc_state {
>  	void *data;			/* Data for callback. */
>  	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
>  };
>  
>  struct vring_desc_state_packed {
> +	void *data;			/* Data for callback. */
> +	struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
> +	int num;			/* Descriptor list length. */
> +	dma_addr_t addr;		/* Buffer DMA addr. */
> +	u32 len;			/* Buffer length. */
> +	u16 flags;			/* Descriptor flags. */
>  	int next;			/* The next desc state. */
>  };
>  
Idea: how about using data to chain these descriptors?
You can validate it's pointing within an array to distinguish
e.g. on detach.

-- 
MST

On Wed, Jul 11, 2018 at 10:27:09AM +0800, Tiwei Bie
wrote:
> This commit introduces the support (without EVENT_IDX) for
> packed ring.
> 
> Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
> ---
>  drivers/virtio/virtio_ring.c | 495 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 487 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index c4f8abc7445a..f317b485ba54 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -55,12 +55,21 @@
>  #define END_USE(vq)
>  #endif
>  
> +#define _VRING_DESC_F_AVAIL(b)	((__u16)(b) << 7)
> +#define _VRING_DESC_F_USED(b)	((__u16)(b) << 15)
> +
>  struct vring_desc_state {
>  	void *data;			/* Data for callback. */
>  	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
>  };
>  
>  struct vring_desc_state_packed {
> +	void *data;			/* Data for callback. */
> +	struct vring_packed_desc *indir_desc; /* Indirect descriptor, if any. */
> +	int num;			/* Descriptor list length. */
> +	dma_addr_t addr;		/* Buffer DMA addr. */
> +	u32 len;			/* Buffer length. */
> +	u16 flags;			/* Descriptor flags. */
>  	int next;			/* The next desc state. */
>  };
>  
> @@ -660,7 +669,6 @@ static bool virtqueue_poll_split(struct virtqueue *_vq,
unsigned last_used_idx)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  
> -	virtio_mb(vq->weak_barriers);
>  	return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev,
vq->vring.used->idx);
>  }
>  
> @@ -757,6 +765,72 @@ static inline unsigned vring_size_packed(unsigned int
num, unsigned long align)
>  		& ~(align - 1)) + sizeof(struct vring_packed_desc_event) * 2;
>  }
>  
> +static void vring_unmap_state_packed(const struct vring_virtqueue *vq,
> +				     struct vring_desc_state_packed *state)
> +{
> +	u16 flags;
> +
> +	if (!vring_use_dma_api(vq->vq.vdev))
> +		return;
> +
> +	flags = state->flags;
> +
> +	if (flags & VRING_DESC_F_INDIRECT) {
> +		dma_unmap_single(vring_dma_dev(vq),
> +				 state->addr, state->len,
> +				 (flags & VRING_DESC_F_WRITE) ?
> +				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
> +	} else {
> +		dma_unmap_page(vring_dma_dev(vq),
> +			       state->addr, state->len,
> +			       (flags & VRING_DESC_F_WRITE) ?
> +			       DMA_FROM_DEVICE : DMA_TO_DEVICE);
> +	}
> +}
> +
> +static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
> +				   struct vring_packed_desc *desc)
> +{
> +	u16 flags;
> +
> +	if (!vring_use_dma_api(vq->vq.vdev))
> +		return;
> +
> +	flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
BTW this stuff is only used on error etc. Is there a way to
reuse vring_unmap_state_packed?
> +
> +	if (flags & VRING_DESC_F_INDIRECT) {
> +		dma_unmap_single(vring_dma_dev(vq),
> +				 virtio64_to_cpu(vq->vq.vdev, desc->addr),
> +				 virtio32_to_cpu(vq->vq.vdev, desc->len),
> +				 (flags & VRING_DESC_F_WRITE) ?
> +				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
> +	} else {
> +		dma_unmap_page(vring_dma_dev(vq),
> +			       virtio64_to_cpu(vq->vq.vdev, desc->addr),
> +			       virtio32_to_cpu(vq->vq.vdev, desc->len),
> +			       (flags & VRING_DESC_F_WRITE) ?
> +			       DMA_FROM_DEVICE : DMA_TO_DEVICE);
> +	}
> +}
> +
> +static struct vring_packed_desc *alloc_indirect_packed(struct virtqueue
*_vq,
> +						       unsigned int total_sg,
> +						       gfp_t gfp)
> +{
> +	struct vring_packed_desc *desc;
> +
> +	/*
> +	 * We require lowmem mappings for the descriptors because
> +	 * otherwise virt_to_phys will give us bogus addresses in the
> +	 * virtqueue.
> +	 */
> +	gfp &= ~__GFP_HIGHMEM;
> +
> +	desc = kmalloc(total_sg * sizeof(struct vring_packed_desc), gfp);
> +
> +	return desc;
> +}
> +
>  static inline int virtqueue_add_packed(struct virtqueue *_vq,
>  				       struct scatterlist *sgs[],
>  				       unsigned int total_sg,
> @@ -766,47 +840,449 @@ static inline int virtqueue_add_packed(struct
virtqueue *_vq,
>  				       void *ctx,
>  				       gfp_t gfp)
>  {
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	struct vring_packed_desc *desc;
> +	struct scatterlist *sg;
> +	unsigned int i, n, descs_used, uninitialized_var(prev), err_idx;
> +	__virtio16 uninitialized_var(head_flags), flags;
> +	u16 head, avail_wrap_counter, id, curr;
> +	bool indirect;
> +
> +	START_USE(vq);
> +
> +	BUG_ON(data == NULL);
> +	BUG_ON(ctx && vq->indirect);
> +
> +	if (unlikely(vq->broken)) {
> +		END_USE(vq);
> +		return -EIO;
> +	}
> +
> +#ifdef DEBUG
> +	{
> +		ktime_t now = ktime_get();
> +
> +		/* No kick or get, with .1 second between?  Warn. */
> +		if (vq->last_add_time_valid)
> +			WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time))
> +					    > 100);
> +		vq->last_add_time = now;
> +		vq->last_add_time_valid = true;
> +	}
> +#endif
> +
> +	BUG_ON(total_sg == 0);
> +
> +	head = vq->next_avail_idx;
> +	avail_wrap_counter = vq->avail_wrap_counter;
> +
> +	if (virtqueue_use_indirect(_vq, total_sg))
> +		desc = alloc_indirect_packed(_vq, total_sg, gfp);
> +	else {
> +		desc = NULL;
> +		WARN_ON_ONCE(total_sg > vq->vring_packed.num &&
!vq->indirect);
> +	}
> +
> +	if (desc) {
> +		/* Use a single buffer which doesn't continue */
> +		indirect = true;
> +		/* Set up rest to use this indirect table. */
> +		i = 0;
> +		descs_used = 1;
> +	} else {
> +		indirect = false;
> +		desc = vq->vring_packed.desc;
> +		i = head;
> +		descs_used = total_sg;
> +	}
> +
> +	if (vq->vq.num_free < descs_used) {
> +		pr_debug("Can't add buf len %i - avail = %i\n",
> +			 descs_used, vq->vq.num_free);
> +		/* FIXME: for historical reasons, we force a notify here if
> +		 * there are outgoing parts to the buffer.  Presumably the
> +		 * host should service the ring ASAP. */
I don't think we have a reason to do this for packed ring.
No historical baggage there, right?
> +		if (out_sgs)
> +			vq->notify(&vq->vq);
> +		if (indirect)
> +			kfree(desc);
> +		END_USE(vq);
> +		return -ENOSPC;
> +	}
> +
> +	id = vq->free_head;
> +	BUG_ON(id == vq->vring_packed.num);
> +
> +	curr = id;
> +	for (n = 0; n < out_sgs + in_sgs; n++) {
> +		for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> +			dma_addr_t addr = vring_map_one_sg(vq, sg, n < out_sgs ?
> +					       DMA_TO_DEVICE : DMA_FROM_DEVICE);
> +			if (vring_mapping_error(vq, addr))
> +				goto unmap_release;
> +
> +			flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT |
> +				  (n < out_sgs ? 0 : VRING_DESC_F_WRITE) |
> +				  _VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
> +				  _VRING_DESC_F_USED(!vq->avail_wrap_counter));
> +			if (!indirect && i == head)
> +				head_flags = flags;
> +			else
> +				desc[i].flags = flags;
> +
> +			desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
> +			desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
> +			i++;
> +			if (!indirect) {
> +				if (vring_use_dma_api(_vq->vdev)) {
> +					vq->desc_state_packed[curr].addr = addr;
> +					vq->desc_state_packed[curr].len > +						sg->length;
> +					vq->desc_state_packed[curr].flags > +					
virtio16_to_cpu(_vq->vdev,
> +								flags);
> +				}
> +				curr = vq->desc_state_packed[curr].next;
> +
> +				if (i >= vq->vring_packed.num) {
> +					i = 0;
> +					vq->avail_wrap_counter ^= 1;
> +				}
> +			}
> +		}
> +	}
> +
> +	prev = (i > 0 ? i : vq->vring_packed.num) - 1;
> +	desc[prev].id = cpu_to_virtio16(_vq->vdev, id);
> +
> +	/* Last one doesn't continue. */
> +	if (total_sg == 1)
> +		head_flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);
> +	else
> +		desc[prev].flags &= cpu_to_virtio16(_vq->vdev,
> +						~VRING_DESC_F_NEXT);
> +
> +	if (indirect) {
> +		/* Now that the indirect table is filled in, map it. */
> +		dma_addr_t addr = vring_map_single(
> +			vq, desc, total_sg * sizeof(struct vring_packed_desc),
> +			DMA_TO_DEVICE);
> +		if (vring_mapping_error(vq, addr))
> +			goto unmap_release;
> +
> +		head_flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_INDIRECT |
> +				      _VRING_DESC_F_AVAIL(avail_wrap_counter) |
> +				      _VRING_DESC_F_USED(!avail_wrap_counter));
> +		vq->vring_packed.desc[head].addr = cpu_to_virtio64(_vq->vdev,
> +								   addr);
> +		vq->vring_packed.desc[head].len = cpu_to_virtio32(_vq->vdev,
> +				total_sg * sizeof(struct vring_packed_desc));
> +		vq->vring_packed.desc[head].id = cpu_to_virtio16(_vq->vdev, id);
> +
> +		if (vring_use_dma_api(_vq->vdev)) {
> +			vq->desc_state_packed[id].addr = addr;
> +			vq->desc_state_packed[id].len = total_sg *
> +					sizeof(struct vring_packed_desc);
> +			vq->desc_state_packed[id].flags > +				
virtio16_to_cpu(_vq->vdev, head_flags);
> +		}
> +	}
> +
> +	/* We're using some buffers from the free list. */
> +	vq->vq.num_free -= descs_used;
> +
> +	/* Update free pointer */
> +	if (indirect) {
> +		n = head + 1;
> +		if (n >= vq->vring_packed.num) {
> +			n = 0;
> +			vq->avail_wrap_counter ^= 1;
> +		}
> +		vq->next_avail_idx = n;
> +		vq->free_head = vq->desc_state_packed[id].next;
> +	} else {
> +		vq->next_avail_idx = i;
> +		vq->free_head = curr;
> +	}
> +
> +	/* Store token and indirect buffer state. */
> +	vq->desc_state_packed[id].num = descs_used;
> +	vq->desc_state_packed[id].data = data;
> +	if (indirect)
> +		vq->desc_state_packed[id].indir_desc = desc;
> +	else
> +		vq->desc_state_packed[id].indir_desc = ctx;
> +
> +	/* A driver MUST NOT make the first descriptor in the list
> +	 * available before all subsequent descriptors comprising
> +	 * the list are made available. */
> +	virtio_wmb(vq->weak_barriers);
> +	vq->vring_packed.desc[head].flags = head_flags;
> +	vq->num_added += descs_used;
> +
> +	pr_debug("Added buffer head %i to %p\n", head, vq);
> +	END_USE(vq);
> +
> +	return 0;
> +
> +unmap_release:
> +	err_idx = i;
> +	i = head;
> +
> +	for (n = 0; n < total_sg; n++) {
> +		if (i == err_idx)
> +			break;
> +		vring_unmap_desc_packed(vq, &desc[i]);
> +		i++;
> +		if (!indirect && i >= vq->vring_packed.num)
> +			i = 0;
> +	}
> +
> +	vq->avail_wrap_counter = avail_wrap_counter;
> +
> +	if (indirect)
> +		kfree(desc);
> +
> +	END_USE(vq);
>  	return -EIO;
>  }
>  
>  static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
>  {
> -	return false;
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 flags;
> +	bool needs_kick;
> +	u32 snapshot;
> +
> +	START_USE(vq);
> +	/* We need to expose the new flags value before checking notification
> +	 * suppressions. */
> +	virtio_mb(vq->weak_barriers);
> +
> +	snapshot = READ_ONCE(*(u32 *)vq->vring_packed.device);
> +	flags = virtio16_to_cpu(_vq->vdev, (__virtio16)(snapshot >> 16))
& 0x3;
> +
> +#ifdef DEBUG
> +	if (vq->last_add_time_valid) {
> +		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
> +					      vq->last_add_time)) > 100);
> +	}
> +	vq->last_add_time_valid = false;
> +#endif
> +
> +	needs_kick = (flags != VRING_EVENT_F_DISABLE);
> +	END_USE(vq);
> +	return needs_kick;
> +}
> +
> +static void detach_buf_packed(struct vring_virtqueue *vq,
> +			      unsigned int id, void **ctx)
> +{
> +	struct vring_desc_state_packed *state = NULL;
> +	struct vring_packed_desc *desc;
> +	unsigned int curr, i;
> +
> +	/* Clear data ptr. */
> +	vq->desc_state_packed[id].data = NULL;
> +
> +	curr = id;
> +	for (i = 0; i < vq->desc_state_packed[id].num; i++) {
> +		state = &vq->desc_state_packed[curr];
> +		vring_unmap_state_packed(vq, state);
> +		curr = state->next;
> +	}
> +
> +	BUG_ON(state == NULL);
> +	vq->vq.num_free += vq->desc_state_packed[id].num;
> +	state->next = vq->free_head;
> +	vq->free_head = id;
> +
> +	if (vq->indirect) {
> +		u32 len;
> +
> +		/* Free the indirect table, if any, now that it's unmapped. */
> +		desc = vq->desc_state_packed[id].indir_desc;
> +		if (!desc)
> +			return;
> +
> +		if (vring_use_dma_api(vq->vq.vdev)) {
> +			len = vq->desc_state_packed[id].len;
> +			for (i = 0; i < len / sizeof(struct vring_packed_desc);
> +					i++)
> +				vring_unmap_desc_packed(vq, &desc[i]);
> +		}
> +		kfree(desc);
> +		vq->desc_state_packed[id].indir_desc = NULL;
> +	} else if (ctx) {
> +		*ctx = vq->desc_state_packed[id].indir_desc;
> +	}
> +}
> +
> +static inline bool is_used_desc_packed(const struct vring_virtqueue *vq,
> +				       u16 idx, bool used_wrap_counter)
> +{
> +	u16 flags;
> +	bool avail, used;
> +
> +	flags = virtio16_to_cpu(vq->vq.vdev,
> +				vq->vring_packed.desc[idx].flags);
> +	avail = !!(flags & VRING_DESC_F_AVAIL);
> +	used = !!(flags & VRING_DESC_F_USED);
> +
> +	return avail == used && used == used_wrap_counter;
>  }
>  
>  static inline bool more_used_packed(const struct vring_virtqueue *vq)
>  {
> -	return false;
> +	return is_used_desc_packed(vq, vq->last_used_idx,
> +			vq->used_wrap_counter);
>  }
>  
>  static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
>  					  unsigned int *len,
>  					  void **ctx)
>  {
> -	return NULL;
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 last_used, id;
> +	void *ret;
> +
> +	START_USE(vq);
> +
> +	if (unlikely(vq->broken)) {
> +		END_USE(vq);
> +		return NULL;
> +	}
> +
> +	if (!more_used_packed(vq)) {
> +		pr_debug("No more buffers in queue\n");
> +		END_USE(vq);
> +		return NULL;
> +	}
> +
> +	/* Only get used elements after they have been exposed by host. */
> +	virtio_rmb(vq->weak_barriers);
> +
> +	last_used = vq->last_used_idx;
> +	id = virtio16_to_cpu(_vq->vdev,
vq->vring_packed.desc[last_used].id);
> +	*len = virtio32_to_cpu(_vq->vdev,
vq->vring_packed.desc[last_used].len);
> +
> +	if (unlikely(id >= vq->vring_packed.num)) {
> +		BAD_RING(vq, "id %u out of range\n", id);
> +		return NULL;
> +	}
> +	if (unlikely(!vq->desc_state_packed[id].data)) {
> +		BAD_RING(vq, "id %u is not a head!\n", id);
> +		return NULL;
> +	}
> +
> +	vq->last_used_idx += vq->desc_state_packed[id].num;
> +	if (vq->last_used_idx >= vq->vring_packed.num) {
> +		vq->last_used_idx -= vq->vring_packed.num;
> +		vq->used_wrap_counter ^= 1;
> +	}
> +
> +	/* detach_buf_packed clears data, so grab it now. */
> +	ret = vq->desc_state_packed[id].data;
> +	detach_buf_packed(vq, id, ctx);
> +
> +#ifdef DEBUG
> +	vq->last_add_time_valid = false;
> +#endif
> +
> +	END_USE(vq);
> +	return ret;
>  }
>  
>  static void virtqueue_disable_cb_packed(struct virtqueue *_vq)
>  {
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	if (vq->event_flags_shadow != VRING_EVENT_F_DISABLE) {
> +		vq->event_flags_shadow = VRING_EVENT_F_DISABLE;
> +		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
> +							vq->event_flags_shadow);
> +	}
>  }
>  
>  static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq)
>  {
> -	return 0;
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	START_USE(vq);
> +
> +	/* We optimistically turn back on interrupts, then check if there was
> +	 * more to do. */
> +
> +	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
> +		vq->event_flags_shadow = VRING_EVENT_F_ENABLE;
> +		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
> +							vq->event_flags_shadow);
> +	}
> +
> +	END_USE(vq);
> +	return vq->last_used_idx | ((u16)vq->used_wrap_counter <<
15);
>  }
>  
> -static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned
last_used_idx)
> +static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned
off_wrap)
>  {
> -	return false;
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	bool wrap_counter;
> +	u16 used_idx;
> +
> +	wrap_counter = off_wrap >> 15;
> +	used_idx = off_wrap & ~(1 << 15);
> +
> +	return is_used_desc_packed(vq, used_idx, wrap_counter);
>  }
>  
>  static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
>  {
> -	return false;
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	START_USE(vq);
> +
> +	/* We optimistically turn back on interrupts, then check if there was
> +	 * more to do. */
> +
> +	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
> +		vq->event_flags_shadow = VRING_EVENT_F_ENABLE;
> +		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
> +							vq->event_flags_shadow);
> +		/* We need to enable interrupts first before re-checking
> +		 * for more used buffers. */
> +		virtio_mb(vq->weak_barriers);
> +	}
> +
> +	if (more_used_packed(vq)) {
> +		END_USE(vq);
> +		return false;
> +	}
> +
> +	END_USE(vq);
> +	return true;
>  }
>  
>  static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
>  {
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	unsigned int i;
> +	void *buf;
> +
> +	START_USE(vq);
> +
> +	for (i = 0; i < vq->vring_packed.num; i++) {
> +		if (!vq->desc_state_packed[i].data)
> +			continue;
> +		/* detach_buf clears data, so grab it now. */
> +		buf = vq->desc_state_packed[i].data;
> +		detach_buf_packed(vq, i, NULL);
> +		END_USE(vq);
> +		return buf;
> +	}
> +	/* That should have freed everything. */
> +	BUG_ON(vq->vq.num_free != vq->vring_packed.num);
> +
> +	END_USE(vq);
>  	return NULL;
>  }
>  
> @@ -1083,6 +1559,9 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned
last_used_idx)
>  {
>  	struct vring_virtqueue *vq = to_vvq(_vq);
>  
> +	/* We need to enable interrupts first before re-checking
> +	 * for more used buffers. */
> +	virtio_mb(vq->weak_barriers);
>  	return vq->packed ? virtqueue_poll_packed(_vq, last_used_idx) :
>  			    virtqueue_poll_split(_vq, last_used_idx);
>  }
> -- 
> 2.18.0