netdev - Re: [PATCH net] virtio-net: drop the multi-buffer XDP packet in zerocopy

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Message-ID: <CACGkMEuHDLJiw=VdX38xqkaS-FJPTAU6+XUNwfGkNZGfp+6tKg@mail.gmail.com>
Date: Wed, 4 Jun 2025 08:37:16 +0800
From: Jason Wang <jasowang@...hat.com>
To: Bui Quang Minh <minhquangbui99@...il.com>
Cc: netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>, 
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez <eperezma@...hat.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "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>, 
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	bpf@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net] virtio-net: drop the multi-buffer XDP packet in zerocopy

On Tue, Jun 3, 2025 at 11:07 PM Bui Quang Minh <minhquangbui99@...il.com> wrote:
>
> In virtio-net, we have not yet supported multi-buffer XDP packet in
> zerocopy mode when there is a binding XDP program. However, in that
> case, when receiving multi-buffer XDP packet, we skip the XDP program
> and return XDP_PASS. As a result, the packet is passed to normal network
> stack which is an incorrect behavior. This commit instead returns
> XDP_DROP in that case.
>
> Fixes: 99c861b44eb1 ("virtio_net: xsk: rx: support recv merge mode")
> Cc: stable@...r.kernel.org
> Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> ---
>  drivers/net/virtio_net.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e53ba600605a..4c35324d6e5b 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1309,9 +1309,14 @@ static struct sk_buff *virtnet_receive_xsk_merge(struct net_device *dev, struct
>         ret = XDP_PASS;

It would be simpler to just assign XDP_DROP here?

Or if you wish to stick to the way, we can simply remove this assignment.

>         rcu_read_lock();
>         prog = rcu_dereference(rq->xdp_prog);
> -       /* TODO: support multi buffer. */
> -       if (prog && num_buf == 1)
> -               ret = virtnet_xdp_handler(prog, xdp, dev, xdp_xmit, stats);
> +       if (prog) {
> +               /* TODO: support multi buffer. */
> +               if (num_buf == 1)
> +                       ret = virtnet_xdp_handler(prog, xdp, dev, xdp_xmit,
> +                                                 stats);
> +               else
> +                       ret = XDP_DROP;
> +       }
>         rcu_read_unlock();
>
>         switch (ret) {
> --
> 2.43.0
>

Thanks