netdev - Re: [PATCH vhost] virtio_net: fix the missing of the dma cpu sync

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Date: Sun, 8 Oct 2023 12:53:19 +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>, netdev@...r.kernel.org, 
	Michael Roth <michael.roth@....com>
Subject: Re: [PATCH vhost] virtio_net: fix the missing of the dma cpu sync

On Wed, Sep 27, 2023 at 1:53 PM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
> Commit 295525e29a5b ("virtio_net: merge dma operations when filling
> mergeable buffers") unmaps the buffer with DMA_ATTR_SKIP_CPU_SYNC when
> the dma->ref is zero. We do that with DMA_ATTR_SKIP_CPU_SYNC, because we
> do not want to do the sync for the entire page_frag. But that misses the
> sync for the current area.
>
> This patch does cpu sync regardless of whether the ref is zero or not.
>
> Fixes: 295525e29a5b ("virtio_net: merge dma operations when filling mergeable buffers")
> Reported-by: Michael Roth <michael.roth@....com>
> Closes: http://lore.kernel.org/all/20230926130451.axgodaa6tvwqs3ut@amd.com
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>

Acked-by: Jason Wang <jasowang@...hat.com>

Thanks

> ---
>  drivers/net/virtio_net.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 98dc9b49d56b..9ece27dc5144 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -589,16 +589,16 @@ static void virtnet_rq_unmap(struct receive_queue *rq, void *buf, u32 len)
>
>         --dma->ref;
>
> -       if (dma->ref) {
> -               if (dma->need_sync && len) {
> -                       offset = buf - (head + sizeof(*dma));
> +       if (dma->need_sync && len) {
> +               offset = buf - (head + sizeof(*dma));
>
> -                       virtqueue_dma_sync_single_range_for_cpu(rq->vq, dma->addr, offset,
> -                                                               len, DMA_FROM_DEVICE);
> -               }
> +               virtqueue_dma_sync_single_range_for_cpu(rq->vq, dma->addr,
> +                                                       offset, len,
> +                                                       DMA_FROM_DEVICE);
> +       }
>
> +       if (dma->ref)
>                 return;
> -       }
>
>         virtqueue_dma_unmap_single_attrs(rq->vq, dma->addr, dma->len,
>                                          DMA_FROM_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
> --
> 2.32.0.3.g01195cf9f
>
>