On Wed, Oct 29, 2025 at 11:09:10AM +0800, Xuan Zhuo wrote:
> The purpose of commit 703eec1b2422 ("virtio_net: fixing XDP for fully
> checksummed packets handling") is to record the flags in advance, as
> their value may be overwritten in the XDP case. However, the flags
> recorded under big mode are incorrect, because in big mode, the passed
> buf does not point to the rx buffer, but rather to the page of the
> submitted buffer. This commit fixes this issue.
>
> For the small mode, the commit c11a49d58ad2 ("virtio_net: Fix mismatched
> buf address when unmapping for small packets") fixed it.
>
> Fixes: 703eec1b2422 ("virtio_net: fixing XDP for fully checksummed packets
> handling")
> Signed-off-by: Xuan Zhuo <[email protected]>
> Acked-by: Jason Wang <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
> ---
> drivers/net/virtio_net.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 8e8a179aaa49..59f116b609f6 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2625,22 +2625,28 @@ static void receive_buf(struct virtnet_info *vi,
> struct receive_queue *rq,
> return;
> }
>
> - /* 1. Save the flags early, as the XDP program might overwrite them.
> + /* About the flags below:
> + * 1. Save the flags early, as the XDP program might overwrite them.
> * These flags ensure packets marked as VIRTIO_NET_HDR_F_DATA_VALID
> * stay valid after XDP processing.
> * 2. XDP doesn't work with partially checksummed packets (refer to
> * virtnet_xdp_set()), so packets marked as
> * VIRTIO_NET_HDR_F_NEEDS_CSUM get dropped during XDP processing.
> */
> - flags = ((struct virtio_net_common_hdr *)buf)->hdr.flags;
>
> - if (vi->mergeable_rx_bufs)
> + if (vi->mergeable_rx_bufs) {
> + flags = ((struct virtio_net_common_hdr *)buf)->hdr.flags;
> skb = receive_mergeable(dev, vi, rq, buf, ctx, len, xdp_xmit,
> stats);
> - else if (vi->big_packets)
> + } else if (vi->big_packets) {
> + void *p = page_address((struct page *)buf);
> +
> + flags = ((struct virtio_net_common_hdr *)p)->hdr.flags;
> skb = receive_big(dev, vi, rq, buf, len, stats);
> - else
> + } else {
> + flags = ((struct virtio_net_common_hdr *)buf)->hdr.flags;
> skb = receive_small(dev, vi, rq, buf, ctx, len, xdp_xmit,
> stats);
> + }
>
> if (unlikely(!skb))
> return;
> --
> 2.32.0.3.g01195cf9f
