[PATCH vhost v2 04/12] virtio_ring: split: support premapped

Xuan Zhuo
2023-03-08T06:44:35Z

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 non-indirect path, if dma_address is used, extra.addr will be
set to DMA_MAPPING_ERROR. So when do unmap, we can pass it.

Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 221ff54fe58b..61deaf0a4faf 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -457,6 +457,9 @@ static unsigned int vring_unmap_one_split(const struct
vring_virtqueue *vq,
 				 (flags & VRING_DESC_F_WRITE) ?
 				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
 	} else {
+		if (extra[i].addr == DMA_MAPPING_ERROR)
+			goto out;
+
 		dma_unmap_page(vring_dma_dev(vq),
 			       extra[i].addr,
 			       extra[i].len,
@@ -497,7 +500,8 @@ static inline unsigned int virtqueue_add_desc_split(struct
virtqueue *vq,
 						    dma_addr_t addr,
 						    unsigned int len,
 						    u16 flags,
-						    bool indirect)
+						    bool indirect,
+						    bool do_map)
 {
 	struct vring_virtqueue *vring = to_vvq(vq);
 	struct vring_desc_extra *extra = vring->split.desc_extra;
@@ -511,7 +515,7 @@ static inline unsigned int virtqueue_add_desc_split(struct
virtqueue *vq,
 		next = extra[i].next;
 		desc[i].next = cpu_to_virtio16(vq->vdev, next);

-		extra[i].addr = addr;
+		extra[i].addr = do_map ? addr : DMA_MAPPING_ERROR;
 		extra[i].len = len;
 		extra[i].flags = flags;
 	} else
@@ -604,7 +608,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	struct scatterlist *sg;
 	struct vring_desc *desc;
 	unsigned int i, n, avail, descs_used, prev;
-	bool indirect;
+	bool indirect, do_map;
 	int head;

 	START_USE(vq);
@@ -657,7 +661,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 		return -ENOSPC;
 	}

-	if (virtqueue_map_sgs(vq, sgs, total_sg, out_sgs, in_sgs))
+	do_map = !sgs[0]->dma_address;
+	if (do_map && virtqueue_map_sgs(vq, sgs, total_sg, out_sgs, in_sgs))
 		return -ENOMEM;

 	for (n = 0; n < out_sgs; n++) {
@@ -670,7 +675,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 						     sg->dma_address,
 						     sg->length,
 						     VRING_DESC_F_NEXT,
-						     indirect);
+						     indirect, do_map);
 		}
 	}
 	for (; n < (out_sgs + in_sgs); n++) {
@@ -684,7 +689,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 						     sg->length,
 						     VRING_DESC_F_NEXT |
 						     VRING_DESC_F_WRITE,
-						     indirect);
+						     indirect, do_map);
 		}
 	}
 	/* Last one doesn't continue. */
@@ -705,7 +710,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 					 head, addr,
 					 total_sg * sizeof(struct vring_desc),
 					 VRING_DESC_F_INDIRECT,
-					 false);
+					 false, true);
 	}

 	/* We're using some buffers from the free list. */
@@ -748,7 +753,8 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 	return 0;

 unmap_release:
-	virtqueue_unmap_sgs(vq, sgs, total_sg, out_sgs, in_sgs);
+	if (do_map)
+		virtqueue_unmap_sgs(vq, sgs, total_sg, out_sgs, in_sgs);

 	if (indirect)
 		kfree(desc);
--
2.32.0.3.g01195cf9f