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

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Date: Wed, 12 Jul 2023 16:33:42 +0800
From: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To: Jason Wang <jasowang@...hat.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 Wed, 12 Jul 2023 16:31:35 +0800, Jason Wang <jasowang@...hat.com> wrote:
> 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?

Here the map operate is for the indirect descs array.

So this is done inside the virtio core.

Thanks.




>
> 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
> >
>