Re: [PATCH vhost v6 01/11] virtio_ring: split: separate dma codes

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On Mon, Mar 27, 2023 at 12:05 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> DMA-related logic is separated from the virtqueue_add_split() to
> one new function. DMA address will be saved as sg->dma_address if
> use_dma_api is true, then virtqueue_add_split() will use it directly.
> Unmap operation will be simpler.
>
> The purpose of this is to facilitate subsequent support to receive
> dma address mapped by drivers.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>

Acked-by: Jason Wang <jasowang@xxxxxxxxxx>

Thanks

> ---
>  drivers/virtio/virtio_ring.c | 122 +++++++++++++++++++++++++++--------
>  1 file changed, 94 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 41144b5246a8..2aafb7da793d 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -379,6 +379,14 @@ static dma_addr_t vring_map_one_sg(const struct vring_virtqueue *vq,
>                             direction);
>  }
>
> +static dma_addr_t vring_sg_address(struct scatterlist *sg)
> +{
> +       if (sg->dma_address)
> +               return sg->dma_address;
> +
> +       return (dma_addr_t)sg_phys(sg);
> +}
> +
>  static dma_addr_t vring_map_single(const struct vring_virtqueue *vq,
>                                    void *cpu_addr, size_t size,
>                                    enum dma_data_direction direction)
> @@ -520,6 +528,80 @@ static inline unsigned int virtqueue_add_desc_split(struct virtqueue *vq,
>         return next;
>  }
>
> +static void virtqueue_unmap_sgs(struct vring_virtqueue *vq,
> +                               struct scatterlist *sgs[],
> +                               unsigned int total_sg,
> +                               unsigned int out_sgs,
> +                               unsigned int in_sgs)
> +{
> +       struct scatterlist *sg;
> +       unsigned int n;
> +
> +       if (!vq->use_dma_api)
> +               return;
> +
> +       for (n = 0; n < out_sgs; n++) {
> +               for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> +                       if (!sg->dma_address)
> +                               return;
> +
> +                       dma_unmap_page(vring_dma_dev(vq), sg->dma_address,
> +                                      sg->length, DMA_TO_DEVICE);
> +               }
> +       }
> +
> +       for (; n < (out_sgs + in_sgs); n++) {
> +               for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> +                       if (!sg->dma_address)
> +                               return;
> +
> +                       dma_unmap_page(vring_dma_dev(vq), sg->dma_address,
> +                                      sg->length, DMA_FROM_DEVICE);
> +               }
> +       }
> +}
> +
> +static int virtqueue_map_sgs(struct vring_virtqueue *vq,
> +                            struct scatterlist *sgs[],
> +                            unsigned int total_sg,
> +                            unsigned int out_sgs,
> +                            unsigned int in_sgs)
> +{
> +       struct scatterlist *sg;
> +       unsigned int n;
> +
> +       if (!vq->use_dma_api)
> +               return 0;
> +
> +       for (n = 0; n < out_sgs; n++) {
> +               for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> +                       dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_TO_DEVICE);
> +
> +                       if (vring_mapping_error(vq, addr))
> +                               goto err;
> +
> +                       sg->dma_address = addr;
> +               }
> +       }
> +
> +       for (; n < (out_sgs + in_sgs); n++) {
> +               for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> +                       dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_FROM_DEVICE);
> +
> +                       if (vring_mapping_error(vq, addr))
> +                               goto err;
> +
> +                       sg->dma_address = addr;
> +               }
> +       }
> +
> +       return 0;
> +
> +err:
> +       virtqueue_unmap_sgs(vq, sgs, total_sg, out_sgs, in_sgs);
> +       return -ENOMEM;
> +}
> +
>  static inline int virtqueue_add_split(struct virtqueue *_vq,
>                                       struct scatterlist *sgs[],
>                                       unsigned int total_sg,
> @@ -532,9 +614,9 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>         struct vring_virtqueue *vq = to_vvq(_vq);
>         struct scatterlist *sg;
>         struct vring_desc *desc;
> -       unsigned int i, n, avail, descs_used, prev, err_idx;
> -       int head;
> +       unsigned int i, n, avail, descs_used, prev;
>         bool indirect;
> +       int head;
>
>         START_USE(vq);
>
> @@ -586,32 +668,30 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>                 return -ENOSPC;
>         }
>
> +       if (virtqueue_map_sgs(vq, sgs, total_sg, out_sgs, in_sgs))
> +               goto err_map;
> +
>         for (n = 0; n < out_sgs; n++) {
>                 for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> -                       dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_TO_DEVICE);
> -                       if (vring_mapping_error(vq, addr))
> -                               goto unmap_release;
> -
>                         prev = i;
>                         /* Note that we trust indirect descriptor
>                          * table since it use stream DMA mapping.
>                          */
> -                       i = virtqueue_add_desc_split(_vq, desc, i, addr, sg->length,
> +                       i = virtqueue_add_desc_split(_vq, desc, i,
> +                                                    vring_sg_address(sg),
> +                                                    sg->length,
>                                                      VRING_DESC_F_NEXT,
>                                                      indirect);
>                 }
>         }
>         for (; n < (out_sgs + in_sgs); n++) {
>                 for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> -                       dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_FROM_DEVICE);
> -                       if (vring_mapping_error(vq, addr))
> -                               goto unmap_release;
> -
>                         prev = i;
>                         /* Note that we trust indirect descriptor
>                          * table since it use stream DMA mapping.
>                          */
> -                       i = virtqueue_add_desc_split(_vq, desc, i, addr,
> +                       i = virtqueue_add_desc_split(_vq, desc, i,
> +                                                    vring_sg_address(sg),
>                                                      sg->length,
>                                                      VRING_DESC_F_NEXT |
>                                                      VRING_DESC_F_WRITE,
> @@ -679,23 +759,9 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>         return 0;
>
>  unmap_release:
> -       err_idx = i;
> -
> -       if (indirect)
> -               i = 0;
> -       else
> -               i = head;
> -
> -       for (n = 0; n < total_sg; n++) {
> -               if (i == err_idx)
> -                       break;
> -               if (indirect) {
> -                       vring_unmap_one_split_indirect(vq, &desc[i]);
> -                       i = virtio16_to_cpu(_vq->vdev, desc[i].next);
> -               } else
> -                       i = vring_unmap_one_split(vq, i);
> -       }
> +       virtqueue_unmap_sgs(vq, sgs, total_sg, out_sgs, in_sgs);
>
> +err_map:
>         if (indirect)
>                 kfree(desc);
>
> --
> 2.32.0.3.g01195cf9f
>

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