[PATCH vhost v2 06/12] virtio_ring: split-indirect: support premapped

Xuan Zhuo
2023-03-08T06:44:37Z

virtio core only supports virtual addresses, dma is completed in virtio
core.

In some scenarios (such as the AF_XDP), the memory is allocated
and DMA is completed in advance, so it is necessary for us to support
passing the DMA address to virtio core.

Drives can use sg->dma_address to pass the mapped dma address to virtio
core. If one sg->dma_address is used then all sgs must use
sg->dma_address,
otherwise all dma_address must be null.

On the indirect path, if dma_address is used, desc_state.indir_desc will
be mixed with VRING_INDIRECT_PREMAPPED. So when do unmap, we can pass it.

Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 66a071e3bdef..11827d2e56a8 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -231,6 +231,18 @@ static void vring_free(struct virtqueue *_vq);
  * Helpers.
  */

+#define VRING_INDIRECT_PREMAPPED  BIT(0)
+
+#define desc_mix_dma_map(do_map, desc) \
+	(do_map ? desc : (typeof(desc))((unsigned long)(desc) |
VRING_INDIRECT_PREMAPPED))
+
+#define desc_rm_dma_map(desc) \
+	((typeof(desc))((unsigned long)(desc) & ~VRING_INDIRECT_PREMAPPED))
+
+#define desc_map_inter(desc) \
+	!((unsigned long)(desc) & VRING_INDIRECT_PREMAPPED)
+
+
 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)

 static inline bool virtqueue_use_indirect(struct vring_virtqueue *vq,
@@ -725,7 +737,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	/* Store token and indirect buffer state. */
 	vq->split.desc_state[head].data = data;
 	if (indirect)
-		vq->split.desc_state[head].indir_desc = desc;
+		vq->split.desc_state[head].indir_desc = desc_mix_dma_map(do_map, desc);
 	else
 		vq->split.desc_state[head].indir_desc = ctx;

@@ -820,22 +832,26 @@ static void detach_buf_split(struct vring_virtqueue *vq,
unsigned int head,
 	vq->vq.num_free++;

 	if (vq->indirect) {
-		struct vring_desc *indir_desc -				vq->split.desc_state[head].indir_desc;
+		struct vring_desc *mix = vq->split.desc_state[head].indir_desc;
+		struct vring_desc *indir_desc;
 		u32 len;

 		/* Free the indirect table, if any, now that it's unmapped. */
-		if (!indir_desc)
+		if (!mix)
 			return;

+		indir_desc = desc_rm_dma_map(mix);
+
 		len = vq->split.desc_extra[head].len;

 		BUG_ON(!(vq->split.desc_extra[head].flags &
 				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_indirect(vq, &indir_desc[j]);
+		if (desc_map_inter(mix)) {
+			for (j = 0; j < len / sizeof(struct vring_desc); j++)
+				vring_unmap_one_split_indirect(vq, &indir_desc[j]);
+		}

 		kfree(indir_desc);
 		vq->split.desc_state[head].indir_desc = NULL;
--
2.32.0.3.g01195cf9f