netdev - Re: [PATCH net-next 5/8] net: implement virtio helpers to handle UDP GSO tunneling.

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Message-ID: <0824bc9f-ac6d-4fe9-9c1b-b0523959741e@redhat.com>
Date: Fri, 23 May 2025 08:44:26 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, netdev@...r.kernel.org
Cc: Jason Wang <jasowang@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, "Michael S. Tsirkin" <mst@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>
Subject: Re: [PATCH net-next 5/8] net: implement virtio helpers to handle UDP
 GSO tunneling.

On 5/23/25 8:09 AM, Paolo Abeni wrote:
> On 5/23/25 12:29 AM, Willem de Bruijn wrote:
>> Paolo Abeni wrote:
>>> +	/* No UDP fragments over UDP tunnel. */
>>
>> What are udp fragments and why is TCP with ECN not supported?
> 
> "udp fragments" is the syncopated form of "UDP datagrams carryed by IP
> fragments". I'll use UFO to be clearer ;)
> 
> The ECN part is cargo cult on my side from my original implementation
> which dates back to ... a lot of time ago. A quick recheck makes me
> think I could drop it. I'll have a better look and either document the
> choice or drop the check in the next revision.

Let me quote the relevant code:

>>> +	gso_inner_type = hdr->gso_type & ~(VIRTIO_NET_HDR_GSO_ECN |
>>> +					   gso_tunnel_type);
>>> +	if (!gso_inner_type || gso_inner_type == VIRTIO_NET_HDR_GSO_UDP)
>>> +		return -EINVAL;

Actually GSO_ECN is allowed. What is _not_ allowed is the GSO_ECN
offload without a paired plain GSO. The intention here is to ensure that
the GSO over UDP tunnel packets actually includes/requires an inner GSO
offload. I'll update the comment accordingly.

Thanks,

Paolo