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

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Message-ID: <f6d7610b-abfe-415d-adf8-08ce791e4e72@gmail.com>
Date: Thu, 5 Jun 2025 21:33:26 +0700
From: Bui Quang Minh <minhquangbui99@...il.com>
To: Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...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>, 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 6/5/25 18:03, Paolo Abeni wrote:
> On 6/3/25 5:06 PM, Bui Quang Minh 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.
> Why? AFAICS the multi-buffer mode depends on features negotiation, which
> is not controlled by the VM user.
>
> Let's suppose the user wants to attach an XDP program to do some per
> packet stats accounting. That suddenly would cause drop packets
> depending on conditions not controlled by the (guest) user. It looks
> wrong to me.

But currently, if a multi-buffer packet arrives, it will not go through 
XDP program so it doesn't increase the stats but still goes to network 
stack. So I think it's not a correct behavior.

>
> XDP_ABORTED looks like a better choice.
>
> /P
>

Thanks,
Quang Minh.