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>

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index bb3d73d..7973814 100644 (file)
--- a/drivers/virtio/virtio_ring.c
+++ b/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);