[RFC v2] virtio: support packed ring

Tiwei Bie
Sun, 01 Apr 2018 14:12:16 -0000

Hello everyone,

This RFC implements packed ring support for virtio driver.

The code was tested with DPDK vhost (testpmd/vhost-PMD) implemented
by Jens at http://dpdk.org/ml/archives/dev/2018-January/089417.html
Minor changes are needed for the vhost code, e.g. to kick the guest.

TODO:
- Refinements and bug fixes;
- Split into small patches;
- Test indirect descriptor support;
- Test/fix event suppression support;
- Test devices other than net;

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!

Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
---
 drivers/virtio/virtio_ring.c       | 1094 +++++++++++++++++++++++++++++-------
 include/linux/virtio_ring.h        |    8 +-
 include/uapi/linux/virtio_config.h |   12 +-
 include/uapi/linux/virtio_ring.h   |   61 ++
 4 files changed, 980 insertions(+), 195 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 71458f493cf8..0515dca34d77 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -58,14 +58,15 @@

 struct vring_desc_state {
 	void *data;			/* Data for callback. */
-	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
+	void *indir_desc;		/* Indirect descriptor, if any. */
+	int num;			/* Descriptor list length. */
 };

 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;
@@ -79,19 +80,45 @@ struct vring_virtqueue {
 	/* Host publishes avail event idx */
 	bool event;

-	/* Head of free buffer list. */
-	unsigned int free_head;
 	/* Number we've added since last sync. */
 	unsigned int num_added;

 	/* 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;
+			/* Head of free buffer list. */
+			unsigned int free_head;
+
+			/* 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. */
+			u8 wrap_counter;
+
+			/* Index of the next avail descriptor. */
+			unsigned int 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);
@@ -201,8 +228,33 @@ 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 void vring_unmap_one_split(const struct vring_virtqueue *vq,
+				  struct vring_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 void vring_unmap_one_packed(const struct vring_virtqueue *vq,
+				   struct vring_packed_desc *desc)
 {
 	u16 flags;

@@ -235,8 +287,9 @@ static int vring_mapping_error(const struct vring_virtqueue
*vq,
 	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;
@@ -257,14 +310,32 @@ 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 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_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;
@@ -303,7 +374,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 	/* 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);
+		desc = alloc_indirect_split(_vq, total_sg, gfp);
 	else {
 		desc = NULL;
 		WARN_ON_ONCE(total_sg > vq->vring.num && !vq->indirect);
@@ -424,7 +495,7 @@ 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);
 	}

@@ -435,6 +506,210 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 	return -EIO;
 }

+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)
+{
+	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;
+	int head, wrap_counter;
+	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;
+	wrap_counter = vq->wrap_counter;
+
+	/* 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_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;
+	}
+
+	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->wrap_counter) |
+					VRING_DESC_F_USED(!vq->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);
+			desc[i].id = cpu_to_virtio32(_vq->vdev, head);
+			prev = i;
+			i++;
+			if (!indirect && i >= vq->vring_packed.num) {
+				i = 0;
+				vq->wrap_counter ^= 1;
+			}
+		}
+	}
+	/* 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(wrap_counter) |
+					     VRING_DESC_F_USED(!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_virtio32(_vq->vdev, head);
+	}
+
+	/* 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->wrap_counter ^= 1;
+		}
+		vq->next_avail_idx = n;
+	} else
+		vq->next_avail_idx = i;
+
+	/* Store token and indirect buffer state. */
+	vq->desc_state[head].num = descs_used;
+	vq->desc_state[head].data = data;
+	if (indirect)
+		vq->desc_state[head].indir_desc = desc;
+	else
+		vq->desc_state[head].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++;
+
+	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_one_packed(vq, &desc[i]);
+		i++;
+		if (!indirect && i >= vq->vring_packed.num)
+			i = 0;
+	}
+
+	vq->wrap_counter = wrap_counter;
+
+	if (indirect)
+		kfree(desc);
+
+	END_USE(vq);
+	return -EIO;
+}
+
+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.
@@ -537,18 +812,7 @@ int virtqueue_add_inbuf_ctx(struct virtqueue *vq,
 }
 EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_ctx);

-/**
- * virtqueue_kick_prepare - first half of split virtqueue_kick call.
- * @vq: the struct virtqueue
- *
- * Instead of virtqueue_kick(), you can do:
- *	if (virtqueue_kick_prepare(vq))
- *		virtqueue_notify(vq);
- *
- * This is sometimes useful because the virtqueue_kick_prepare() needs
- * to be serialized, but the actual virtqueue_notify() call does not.
- */
-bool virtqueue_kick_prepare(struct virtqueue *_vq)
+static bool virtqueue_kick_prepare_split(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	u16 new, old;
@@ -580,6 +844,62 @@ bool virtqueue_kick_prepare(struct virtqueue *_vq)
 	END_USE(vq);
 	return needs_kick;
 }
+
+static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	u16 new, old, off_wrap;
+	bool needs_kick;
+
+	START_USE(vq);
+	/* We need to expose the new flags value before checking notification
+	 * suppressions. */
+	virtio_mb(vq->weak_barriers);
+
+	old = vq->next_avail_idx - vq->num_added;
+	new = vq->next_avail_idx;
+	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
+
+	off_wrap = virtio16_to_cpu(_vq->vdev,
vq->vring_packed.device->off_wrap);
+
+	if (vq->event) {
+		// FIXME: fix this!
+		needs_kick = ((off_wrap >> 15) == vq->wrap_counter) &&
+			     vring_need_event(off_wrap & ~(1<<15), new, old);
+	} else {
+		needs_kick = (vq->vring_packed.device->flags !+
cpu_to_virtio16(_vq->vdev, VRING_EVENT_F_DISABLE));
+	}
+	END_USE(vq);
+	return needs_kick;
+}
+
+/**
+ * virtqueue_kick_prepare - first half of split virtqueue_kick call.
+ * @vq: the struct virtqueue
+ *
+ * Instead of virtqueue_kick(), you can do:
+ *	if (virtqueue_kick_prepare(vq))
+ *		virtqueue_notify(vq);
+ *
+ * This is sometimes useful because the virtqueue_kick_prepare() needs
+ * to be serialized, but the actual virtqueue_notify() call does not.
+ */
+bool virtqueue_kick_prepare(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	return vq->packed ? virtqueue_kick_prepare_packed(_vq) :
+			    virtqueue_kick_prepare_split(_vq);
+}
 EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);

 /**
@@ -626,8 +946,8 @@ bool virtqueue_kick(struct virtqueue *vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_kick);

-static void detach_buf(struct vring_virtqueue *vq, unsigned int head,
-		       void **ctx)
+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);
@@ -639,12 +959,12 @@ static void detach_buf(struct vring_virtqueue *vq,
unsigned int head,
 	i = head;

 	while (vq->vring.desc[i].flags & nextflag) {
-		vring_unmap_one(vq, &vq->vring.desc[i]);
+		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(vq, &vq->vring.desc[i]);
+	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;

@@ -666,7 +986,7 @@ static void detach_buf(struct vring_virtqueue *vq, unsigned
int head,
 		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]);
+			vring_unmap_one_split(vq, &indir_desc[j]);

 		kfree(indir_desc);
 		vq->desc_state[head].indir_desc = NULL;
@@ -675,11 +995,207 @@ static void detach_buf(struct vring_virtqueue *vq,
unsigned int head,
 	}
 }

-static inline bool more_used(const struct vring_virtqueue *vq)
+static int detach_buf_packed(struct vring_virtqueue *vq, unsigned int head,
+			      void **ctx)
+{
+	struct vring_packed_desc *desc;
+	unsigned int i, j;
+
+	/* Clear data ptr. */
+	vq->desc_state[head].data = NULL;
+
+	i = head;
+
+	for (j = 0; j < vq->desc_state[head].num; j++) {
+		desc = &vq->vring_packed.desc[i];
+		vring_unmap_one_packed(vq, desc);
+		desc->flags = 0x0;
+		i++;
+		if (i >= vq->vring_packed.num)
+			i = 0;
+	}
+
+	vq->vq.num_free += vq->desc_state[head].num;
+
+	if (vq->indirect) {
+		u32 len;
+
+		desc = vq->desc_state[head].indir_desc;
+		/* Free the indirect table, if any, now that it's unmapped. */
+		if (!desc)
+			goto out;
+
+		len = virtio32_to_cpu(vq->vq.vdev,
+				      vq->vring_packed.desc[head].len);
+
+		BUG_ON(!(vq->vring_packed.desc[head].flags &
+			 cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT)));
+		BUG_ON(len == 0 || len % sizeof(struct vring_packed_desc));
+
+		for (j = 0; j < len / sizeof(struct vring_packed_desc); j++)
+			vring_unmap_one_packed(vq, &desc[j]);
+
+		kfree(desc);
+		vq->desc_state[head].indir_desc = NULL;
+	} else if (ctx) {
+		*ctx = vq->desc_state[head].indir_desc;
+	}
+
+out:
+	return vq->desc_state[head].num;
+}
+
+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 inline bool more_used_packed(const struct vring_virtqueue *vq)
+{
+	u16 last_used, flags;
+	bool avail, used;
+
+	if (vq->vq.num_free == vq->vring_packed.num)
+		return false;
+
+	last_used = vq->last_used_idx;
+	flags = virtio16_to_cpu(vq->vq.vdev,
+				vq->vring_packed.desc[last_used].flags);
+	avail = flags & VRING_DESC_F_AVAIL(1);
+	used = flags & VRING_DESC_F_USED(1);
+
+	return avail == used;
+}
+
+static inline bool more_used(const struct vring_virtqueue *vq)
+{
+	return vq->packed ? more_used_packed(vq) : more_used_split(vq);
+}
+
+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(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;
+}
+
+void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, unsigned int *len,
+				   void **ctx)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	uint16_t wrap_counter;
+	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 elements after they have been exposed by host. */
+	virtio_rmb(vq->weak_barriers);
+
+	last_used = vq->last_used_idx;
+	i = virtio32_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(i >= vq->vring_packed.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_packed clears data, so grab it now. */
+	ret = vq->desc_state[i].data;
+	detach_buf_packed(vq, i, ctx);
+
+	vq->last_used_idx += vq->desc_state[i].num;
+	if (vq->last_used_idx >= vq->vring_packed.num)
+		vq->last_used_idx -= vq->vring_packed.num;
+
+	wrap_counter = vq->wrap_counter;
+	if (vq->last_used_idx > vq->next_avail_idx)
+		wrap_counter ^= 1;
+
+	/* 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 |
+						wrap_counter << 15));
+
+#ifdef DEBUG
+	vq->last_add_time_valid = false;
+#endif
+
+	END_USE(vq);
+	return ret;
+}
+
 /**
  * virtqueue_get_buf - get the next used buffer
  * @vq: the struct virtqueue we're talking about.
@@ -700,57 +1216,9 @@ 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);

@@ -759,6 +1227,29 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned
int *len)
 	return virtqueue_get_buf_ctx(_vq, len, NULL);
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_buf);
+
+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 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);
+	}
+}
+
 /**
  * virtqueue_disable_cb - disable callbacks
  * @vq: the struct virtqueue we're talking about.
@@ -772,15 +1263,66 @@ 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);

+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 unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	u16 last_used_idx, wrap_counter, off_wrap;
+
+	START_USE(vq);
+
+	last_used_idx = vq->last_used_idx;
+	wrap_counter = vq->wrap_counter;
+
+	if (last_used_idx > vq->next_avail_idx)
+		wrap_counter ^= 1;
+
+	off_wrap = last_used_idx | (wrap_counter << 15);
+
+	/* 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->event_flags_shadow == VRING_EVENT_F_DISABLE) {
+		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);
+	}
+	vq->vring_packed.driver->off_wrap = cpu_to_virtio16(_vq->vdev,
off_wrap);
+	END_USE(vq);
+	return last_used_idx;
+}
+
 /**
  * virtqueue_enable_cb_prepare - restart callbacks after disable_cb
  * @vq: the struct virtqueue we're talking about.
@@ -796,26 +1338,34 @@ 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);

+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_poll_packed(struct virtqueue *_vq, unsigned
last_used_idx)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	bool avail, used;
+	u16 flags;
+
+	virtio_mb(vq->weak_barriers);
+	flags = virtio16_to_cpu(vq->vq.vdev,
+			vq->vring_packed.desc[last_used_idx].flags);
+	avail = flags & VRING_DESC_F_AVAIL(1);
+	used = flags & VRING_DESC_F_USED(1);
+	return avail == used;
+}
+
 /**
  * virtqueue_poll - query pending used buffers
  * @vq: the struct virtqueue we're talking about.
@@ -829,8 +1379,8 @@ 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);

@@ -852,6 +1402,83 @@ bool virtqueue_enable_cb(struct virtqueue *_vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_enable_cb);

+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 bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	u16 bufs, off_wrap, used_idx, wrap_counter;
+
+	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->event_flags_shadow == VRING_EVENT_F_DISABLE) {
+		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);
+	}
+
+	/* TODO: tune this threshold */
+	bufs = (u16)(vq->next_avail_idx - vq->last_used_idx) * 3 / 4;
+
+	used_idx = vq->last_used_idx + bufs;
+	if (used_idx >= vq->vring_packed.num)
+		used_idx -= vq->vring_packed.num;
+
+	wrap_counter = vq->wrap_counter;
+	if (used_idx > vq->next_avail_idx)
+		wrap_counter ^= 1;
+
+	off_wrap = used_idx | (wrap_counter << 15);
+
+	virtio_store_mb(vq->weak_barriers,
&vq->vring_packed.driver->off_wrap,
+			cpu_to_virtio16(_vq->vdev, off_wrap));
+
+	if (more_used_packed(vq)) {
+		END_USE(vq);
+		return false;
+	}
+
+	END_USE(vq);
+	return true;
+}
+
 /**
  * virtqueue_enable_cb_delayed - restart callbacks after disable_cb.
  * @vq: the struct virtqueue we're talking about.
@@ -868,37 +1495,69 @@ 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);

+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;
+}
+
+static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	unsigned int i, num;
+	void *buf;
+
+	START_USE(vq);
+
+	for (i = 0; i < vq->vring_packed.num; i++) {
+		if (!vq->desc_state[i].data)
+			continue;
+		/* detach_buf clears data, so grab it now. */
+		buf = vq->desc_state[i].data;
+		num = detach_buf_packed(vq, i, NULL);
+		if (vq->next_avail_idx < num) {
+			vq->next_avail_idx = vq->vring_packed.num -
+					(num - vq->next_avail_idx);
+			vq->wrap_counter ^= 1;
+		} else {
+			vq->next_avail_idx -= num;
+		}
+		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;
+}
+
 /**
  * virtqueue_detach_unused_buf - detach first unused buffer
  * @vq: the struct virtqueue we're talking about.
@@ -910,27 +1569,9 @@ 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);

@@ -955,7 +1596,8 @@ 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,
@@ -963,19 +1605,20 @@ struct virtqueue *__vring_new_virtqueue(unsigned int
index,
 					void (*callback)(struct virtqueue *),
 					const char *name)
 {
-	unsigned int i;
+	unsigned int num, i;
 	struct vring_virtqueue *vq;

-	vq = kmalloc(sizeof(*vq) + vring.num * sizeof(struct vring_desc_state),
+	num = packed ? vring.vring_packed.num : vring.vring_split.num;
+
+	vq = kmalloc(sizeof(*vq) + num * sizeof(struct vring_desc_state),
 		     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;
@@ -984,9 +1627,8 @@ 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;
@@ -997,18 +1639,37 @@ 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->wrap_counter = 1;
+		vq->event_flags_shadow = 0;
+	} 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);
+	}
+
 	/* 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));
+	memset(vq->desc_state, 0, num * sizeof(struct vring_desc_state));

 	return &vq->vq;
 }
@@ -1056,6 +1717,22 @@ 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_packed_size(num, align) : vring_size(num, align);
+}
+
+static inline void vring_packed_init(struct vring_packed *vr, unsigned int num,
+				     void *p, unsigned long align)
+{
+	vr->num = num;
+	vr->desc = p;
+	vr->driver = (void *)(((uintptr_t)p + sizeof(struct vring_packed_desc)
+		* num + align - 1) & ~(align - 1));
+	vr->device = vr->driver + 1;
+}
+
 struct virtqueue *vring_create_virtqueue(
 	unsigned int index,
 	unsigned int num,
@@ -1072,7 +1749,8 @@ 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)) {
@@ -1080,9 +1758,13 @@ 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)
@@ -1094,17 +1776,21 @@ 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_packed_init(&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);
@@ -1130,10 +1816,17 @@ 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_packed_init(&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);

@@ -1143,7 +1836,9 @@ 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);
@@ -1157,14 +1852,18 @@ void vring_transport_features(struct virtio_device
*vdev)

 	for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
 		switch (i) {
-		case VIRTIO_RING_F_INDIRECT_DESC:
+#if 0
+		case VIRTIO_RING_F_INDIRECT_DESC: // FIXME not tested yet.
 			break;
-		case VIRTIO_RING_F_EVENT_IDX:
+		case VIRTIO_RING_F_EVENT_IDX: // FIXME probably not work.
 			break;
+#endif
 		case VIRTIO_F_VERSION_1:
 			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);
@@ -1185,7 +1884,7 @@ 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);

@@ -1228,6 +1927,10 @@ 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);
 }
@@ -1239,11 +1942,16 @@ 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 bbf32524ab27..a0075894ad16 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,
diff --git a/include/uapi/linux/virtio_config.h
b/include/uapi/linux/virtio_config.h
index 308e2096291f..a6e392325e3a 100644
--- a/include/uapi/linux/virtio_config.h
+++ b/include/uapi/linux/virtio_config.h
@@ -49,7 +49,7 @@
  * transport being used (eg. virtio_ring), the rest are per-device feature
  * bits. */
 #define VIRTIO_TRANSPORT_F_START	28
-#define VIRTIO_TRANSPORT_F_END		34
+#define VIRTIO_TRANSPORT_F_END		36

 #ifndef VIRTIO_CONFIG_NO_LEGACY
 /* Do we get callbacks when the ring is completely used, even if we've
@@ -71,4 +71,14 @@
  * this is for compatibility with legacy systems.
  */
 #define VIRTIO_F_IOMMU_PLATFORM		33
+
+/* This feature indicates support for the packed virtqueue layout. */
+#define VIRTIO_F_RING_PACKED		34
+
+/*
+ * This feature indicates that all buffers are used by the device
+ * in the same order in which they have been made available.
+ */
+#define VIRTIO_F_IN_ORDER		35
+
 #endif /* _UAPI_LINUX_VIRTIO_CONFIG_H */
diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
index 6d5d5faa989b..735d4207c988 100644
--- a/include/uapi/linux/virtio_ring.h
+++ b/include/uapi/linux/virtio_ring.h
@@ -44,6 +44,9 @@
 /* This means the buffer contains a list of buffer descriptors. */
 #define VRING_DESC_F_INDIRECT	4

+#define VRING_DESC_F_AVAIL(b)	((b) << 7)
+#define VRING_DESC_F_USED(b)	((b) << 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 +56,10 @@
  * optimization.  */
 #define VRING_AVAIL_F_NO_INTERRUPT	1

+#define VRING_EVENT_F_ENABLE	0x0
+#define VRING_EVENT_F_DISABLE	0x1
+#define VRING_EVENT_F_DESC	0x2
+
 /* We support indirect buffer descriptors */
 #define VIRTIO_RING_F_INDIRECT_DESC	28

@@ -171,4 +178,58 @@ 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 {
+	/* __virtio16 off  : 15; // Descriptor Event Offset
+	 * __virtio16 wrap : 1;  // Descriptor Event Wrap Counter */
+	__virtio16 off_wrap;
+	/* __virtio16 flags : 2; // Descriptor 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;
+};
+
+/* The standard 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 unsigned vring_packed_size(unsigned int num, unsigned long align)
+{
+	return ((sizeof(struct vring_packed_desc) * num + align - 1)
+		& ~(align - 1)) + sizeof(struct vring_packed_desc_event) * 2;
+}
+
 #endif /* _UAPI_LINUX_VIRTIO_RING_H */
--
2.11.0