virtio_ring: skip unmap for premapped

Now we add a case where we skip dma unmap, the vq->premapped is true.

We can't just rely on use_dma_api to determine whether to skip the dma
operation. For convenience, I introduced the "do_unmap". By default, it
is the same as use_dma_api. If the driver is configured with premapped,
then do_unmap is false.

So as long as do_unmap is false, for addr of desc, we should skip dma
unmap operation.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Message-Id: <20230810123057.43407-7-xuanzhuo@linux.alibaba.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_ring.c

@@ -175,6 +175,11 @@ struct vring_virtqueue {
 	/* Do DMA mapping by driver */
 	bool premapped;
 
+	/* Do unmap or not for desc. Just when premapped is False and
+	 * use_dma_api is true, this is true.
+	 */
+	bool do_unmap;
+
 	/* Head of free buffer list. */
 	unsigned int free_head;
 	/* Number we've added since last sync. */
@@ -440,7 +445,7 @@ static void vring_unmap_one_split_indirect(const struct vring_virtqueue *vq,
 {
 	u16 flags;
 
-	if (!vq->use_dma_api)
+	if (!vq->do_unmap)
 		return;
 
 	flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
@@ -458,18 +463,21 @@ static unsigned int vring_unmap_one_split(const struct vring_virtqueue *vq,
 	struct vring_desc_extra *extra = vq->split.desc_extra;
 	u16 flags;
 
-	if (!vq->use_dma_api)
-		goto out;
-
 	flags = extra[i].flags;
 
 	if (flags & VRING_DESC_F_INDIRECT) {
+		if (!vq->use_dma_api)
+			goto out;
+
 		dma_unmap_single(vring_dma_dev(vq),
 				 extra[i].addr,
 				 extra[i].len,
 				 (flags & VRING_DESC_F_WRITE) ?
 				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
 	} else {
+		if (!vq->do_unmap)
+			goto out;
+
 		dma_unmap_page(vring_dma_dev(vq),
 			       extra[i].addr,
 			       extra[i].len,
@@ -635,7 +643,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	}
 	/* Last one doesn't continue. */
 	desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);
-	if (!indirect && vq->use_dma_api)
+	if (!indirect && vq->do_unmap)
 		vq->split.desc_extra[prev & (vq->split.vring.num - 1)].flags &=
 			~VRING_DESC_F_NEXT;
 
@@ -794,7 +802,7 @@ static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
 				VRING_DESC_F_INDIRECT));
 		BUG_ON(len == 0 || len % sizeof(struct vring_desc));
 
-		if (vq->use_dma_api) {
+		if (vq->do_unmap) {
 			for (j = 0; j < len / sizeof(struct vring_desc); j++)
 				vring_unmap_one_split_indirect(vq, &indir_desc[j]);
 		}
@@ -1217,17 +1225,20 @@ static void vring_unmap_extra_packed(const struct vring_virtqueue *vq,
 {
 	u16 flags;
 
-	if (!vq->use_dma_api)
-		return;
-
 	flags = extra->flags;
 
 	if (flags & VRING_DESC_F_INDIRECT) {
+		if (!vq->use_dma_api)
+			return;
+
 		dma_unmap_single(vring_dma_dev(vq),
 				 extra->addr, extra->len,
 				 (flags & VRING_DESC_F_WRITE) ?
 				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
 	} else {
+		if (!vq->do_unmap)
+			return;
+
 		dma_unmap_page(vring_dma_dev(vq),
 			       extra->addr, extra->len,
 			       (flags & VRING_DESC_F_WRITE) ?
@@ -1240,7 +1251,7 @@ static void vring_unmap_desc_packed(const struct vring_virtqueue *vq,
 {
 	u16 flags;
 
-	if (!vq->use_dma_api)
+	if (!vq->do_unmap)
 		return;
 
 	flags = le16_to_cpu(desc->flags);
@@ -1329,7 +1340,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
 				sizeof(struct vring_packed_desc));
 	vq->packed.vring.desc[head].id = cpu_to_le16(id);
 
-	if (vq->use_dma_api) {
+	if (vq->do_unmap) {
 		vq->packed.desc_extra[id].addr = addr;
 		vq->packed.desc_extra[id].len = total_sg *
 				sizeof(struct vring_packed_desc);
@@ -1470,7 +1481,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
 			desc[i].len = cpu_to_le32(sg->length);
 			desc[i].id = cpu_to_le16(id);
 
-			if (unlikely(vq->use_dma_api)) {
+			if (unlikely(vq->do_unmap)) {
 				vq->packed.desc_extra[curr].addr = addr;
 				vq->packed.desc_extra[curr].len = sg->length;
 				vq->packed.desc_extra[curr].flags =
@@ -1604,7 +1615,7 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
 	vq->free_head = id;
 	vq->vq.num_free += state->num;
 
-	if (unlikely(vq->use_dma_api)) {
+	if (unlikely(vq->do_unmap)) {
 		curr = id;
 		for (i = 0; i < state->num; i++) {
 			vring_unmap_extra_packed(vq,
@@ -1621,7 +1632,7 @@ static void detach_buf_packed(struct vring_virtqueue *vq,
 		if (!desc)
 			return;
 
-		if (vq->use_dma_api) {
+		if (vq->do_unmap) {
 			len = vq->packed.desc_extra[id].len;
 			for (i = 0; i < len / sizeof(struct vring_packed_desc);
 					i++)
@@ -2080,6 +2091,7 @@ static struct virtqueue *vring_create_virtqueue_packed(
 	vq->dma_dev = dma_dev;
 	vq->use_dma_api = vring_use_dma_api(vdev);
 	vq->premapped = false;
+	vq->do_unmap = vq->use_dma_api;
 
 	vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
 		!context;
@@ -2587,6 +2599,7 @@ static struct virtqueue *__vring_new_virtqueue(unsigned int index,
 	vq->dma_dev = dma_dev;
 	vq->use_dma_api = vring_use_dma_api(vdev);
 	vq->premapped = false;
+	vq->do_unmap = vq->use_dma_api;
 
 	vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
 		!context;
@@ -2771,6 +2784,7 @@ int virtqueue_set_dma_premapped(struct virtqueue *_vq)
 	}
 
 	vq->premapped = true;
+	vq->do_unmap = false;
 
 	END_USE(vq);