[PATCH RFC 4/5] vhost-vdpa: support IOTLB batching hints

Jason Wang
Thu, 18 Jun 2020 05:56:25 -0000

This patches extend the vhost IOTLB API to accept batch updating hints
form userspace. When userspace wants update the device IOTLB in a
batch, it may do:

1) Write vhost_iotlb_msg with VHOST_IOTLB_BATCH_BEGIN flag
2) Perform a batch of IOTLB updating via VHOST_IOTLB_UPDATE/INVALIDATE
3) Write vhost_iotlb_msg with VHOST_IOTLB_BATCH_END flag

Vhost-vdpa may decide to batch the IOMMU/IOTLB updating in step 3 when
vDPA device support set_map() ops. This is useful for the vDPA device
that want to know all the mappings to tweak their own DMA translation
logic.

For vDPA device that doesn't require set_map(), no behavior changes.

This capability is advertised via VHOST_BACKEND_F_IOTLB_BATCH capability.

Signed-off-by: Jason Wang <jasowang at redhat.com>
---
 drivers/vhost/vdpa.c             | 30 +++++++++++++++++++++++-------
 include/uapi/linux/vhost.h       |  2 ++
 include/uapi/linux/vhost_types.h |  7 +++++++
 3 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 453057421f80..8f624bbafee7 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -56,7 +56,9 @@ enum {
 };

 enum {
-	VHOST_VDPA_BACKEND_FEATURES = (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2)
+	VHOST_VDPA_BACKEND_FEATURES +	(1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2) |
+	(1ULL << VHOST_BACKEND_F_IOTLB_BATCH),
 };

 /* Currently, only network backend w/o multiqueue is supported. */
@@ -77,6 +79,7 @@ struct vhost_vdpa {
 	int virtio_id;
 	int minor;
 	struct eventfd_ctx *config_ctx;
+	int in_batch;
 };

 static DEFINE_IDA(vhost_vdpa_ida);
@@ -125,6 +128,7 @@ static void vhost_vdpa_reset(struct vhost_vdpa *v)
 	const struct vdpa_config_ops *ops = vdpa->config;

 	ops->set_status(vdpa, 0);
+	v->in_batch = 0;
 }

 static long vhost_vdpa_get_device_id(struct vhost_vdpa *v, u8 __user *argp)
@@ -540,9 +544,10 @@ static int vhost_vdpa_map(struct vhost_vdpa *v,

 	if (ops->dma_map)
 		r = ops->dma_map(vdpa, iova, size, pa, perm);
-	else if (ops->set_map)
-		r = ops->set_map(vdpa, dev->iotlb);
-	else
+	else if (ops->set_map) {
+		if (!v->in_batch)
+			r = ops->set_map(vdpa, dev->iotlb);
+	} else
 		r = iommu_map(v->domain, iova, pa, size,
 			      perm_to_iommu_flags(perm));

@@ -559,9 +564,10 @@ static void vhost_vdpa_unmap(struct vhost_vdpa *v, u64
iova, u64 size)

 	if (ops->dma_map)
 		ops->dma_unmap(vdpa, iova, size);
-	else if (ops->set_map)
-		ops->set_map(vdpa, dev->iotlb);
-	else
+	else if (ops->set_map) {
+		if (!v->in_batch)
+			ops->set_map(vdpa, dev->iotlb);
+	} else
 		iommu_unmap(v->domain, iova, size);
 }

@@ -655,6 +661,8 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev
*dev,
 					struct vhost_iotlb_msg *msg)
 {
 	struct vhost_vdpa *v = container_of(dev, struct vhost_vdpa, vdev);
+	struct vdpa_device *vdpa = v->vdpa;
+	const struct vdpa_config_ops *ops = vdpa->config;
 	int r = 0;

 	r = vhost_dev_check_owner(dev);
@@ -668,6 +676,14 @@ static int vhost_vdpa_process_iotlb_msg(struct vhost_dev
*dev,
 	case VHOST_IOTLB_INVALIDATE:
 		vhost_vdpa_unmap(v, msg->iova, msg->size);
 		break;
+	case VHOST_IOTLB_BATCH_BEGIN:
+		v->in_batch = true;
+		break;
+	case VHOST_IOTLB_BATCH_END:
+		if (v->in_batch && ops->set_map)
+			ops->set_map(vdpa, dev->iotlb);
+		v->in_batch = false;
+		break;
 	default:
 		r = -EINVAL;
 		break;
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index 0c2349612e77..565da96f55d5 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -91,6 +91,8 @@

 /* Use message type V2 */
 #define VHOST_BACKEND_F_IOTLB_MSG_V2 0x1
+/* IOTLB can accpet batching hints */
+#define VHOST_BACKEND_F_IOTLB_BATCH  0x2

 #define VHOST_SET_BACKEND_FEATURES _IOW(VHOST_VIRTIO, 0x25, __u64)
 #define VHOST_GET_BACKEND_FEATURES _IOR(VHOST_VIRTIO, 0x26, __u64)
diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
index 669457ce5c48..5c12faffdde9 100644
--- a/include/uapi/linux/vhost_types.h
+++ b/include/uapi/linux/vhost_types.h
@@ -60,6 +60,13 @@ struct vhost_iotlb_msg {
 #define VHOST_IOTLB_UPDATE         2
 #define VHOST_IOTLB_INVALIDATE     3
 #define VHOST_IOTLB_ACCESS_FAIL    4
+/* VHOST_IOTLB_BATCH_BEGIN is a hint that userspace will update
+ * several mappings afterwards. VHOST_IOTLB_BATCH_END is a hint that
+ * userspace had finished the mapping updating. When those two flags
+ * were set, kernel will ignore the rest fileds of the IOTLB message.
+ */
+#define VHOST_IOTLB_BATCH_BEGIN    5
+#define VHOST_IOTLB_BATCH_END      6
 	__u8 type;
 };

--
2.20.1