On Wed, Mar 8, 2023 at 2:44 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> 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
Should be "DMA mapping is completed".
> 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.
"must be null when passing it to virtqueue_add_sgs()"?
>
> On the non-indirect path,
Should it be "direct desc path"?
> if dma_address is used, extra.addr will be
> set to DMA_MAPPING_ERROR. So when do unmap, we can pass it.
I don't get the meaning of "pass" here. Or do you mean
DMA_MAPING_ERROR is a hint that the desc is mapped by the upper layer
instead of the virtio core?
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> ---
> 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;
Any reason we don't need to do the same for indirect descriptors?
Thanks
> 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
>
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