netdev - Re: [PATCH vhost v11 04/10] virtio_ring: support add premapped buf

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Date: Wed, 12 Jul 2023 16:31:35 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: virtualization@...ts.linux-foundation.org, 
	"Michael S. Tsirkin" <mst@...hat.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, 
	John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org, bpf@...r.kernel.org, 
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH vhost v11 04/10] virtio_ring: support add premapped buf

On Mon, Jul 10, 2023 at 11:42 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> If the vq is the premapped mode, use the sg_dma_address() directly.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  drivers/virtio/virtio_ring.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 5ace4539344c..d471dee3f4f7 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -361,6 +361,11 @@ static struct device *vring_dma_dev(const struct vring_virtqueue *vq)
>  static int vring_map_one_sg(const struct vring_virtqueue *vq, struct scatterlist *sg,
>                             enum dma_data_direction direction, dma_addr_t *addr)
>  {
> +       if (vq->premapped) {
> +               *addr = sg_dma_address(sg);
> +               return 0;
> +       }
> +
>         if (!vq->use_dma_api) {
>                 /*
>                  * If DMA is not used, KMSAN doesn't know that the scatterlist
> @@ -639,8 +644,12 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>                 dma_addr_t addr = vring_map_single(
>                         vq, desc, total_sg * sizeof(struct vring_desc),
>                         DMA_TO_DEVICE);
> -               if (vring_mapping_error(vq, addr))
> +               if (vring_mapping_error(vq, addr)) {
> +                       if (vq->premapped)
> +                               goto free_indirect;

Under which case could we hit this? A bug of the driver?

Thanks

> +
>                         goto unmap_release;
> +               }
>
>                 virtqueue_add_desc_split(_vq, vq->split.vring.desc,
>                                          head, addr,
> @@ -706,6 +715,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
>                         i = vring_unmap_one_split(vq, i);
>         }
>
> +free_indirect:
>         if (indirect)
>                 kfree(desc);
>
> @@ -1307,8 +1317,12 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>         addr = vring_map_single(vq, desc,
>                         total_sg * sizeof(struct vring_packed_desc),
>                         DMA_TO_DEVICE);
> -       if (vring_mapping_error(vq, addr))
> +       if (vring_mapping_error(vq, addr)) {
> +               if (vq->premapped)
> +                       goto free_desc;
> +
>                 goto unmap_release;
> +       }
>
>         vq->packed.vring.desc[head].addr = cpu_to_le64(addr);
>         vq->packed.vring.desc[head].len = cpu_to_le32(total_sg *
> @@ -1366,6 +1380,7 @@ static int virtqueue_add_indirect_packed(struct vring_virtqueue *vq,
>         for (i = 0; i < err_idx; i++)
>                 vring_unmap_desc_packed(vq, &desc[i]);
>
> +free_desc:
>         kfree(desc);
>
>         END_USE(vq);
> --
> 2.32.0.3.g01195cf9f
>