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

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Message-ID: <0bc8547d-aa8f-4d96-9191-fd52d1bec74e@gmail.com>
Date: Wed, 4 Jun 2025 21:17:09 +0700
From: Bui Quang Minh <minhquangbui99@...il.com>
To: Jason Wang <jasowang@...hat.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 6/4/25 07:37, Jason Wang wrote:
> 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.

This XDP_PASS is returned for the case when there is no XDP program 
binding (!prog).

>
>>          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
>

Thanks,
Quang Minh.