netdev - Re: [PATCH v6 net-next 0/9] virtio: introduce GSO over UDP tunnel

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Message-ID: <41eb8d72-bfa3-4063-88af-1ec23593b0f8@redhat.com>
Date: Tue, 8 Jul 2025 09:12:04 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: netdev@...r.kernel.org
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 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>, Yuri Benditovich <yuri.benditovich@...nix.com>,
 Akihiko Odaki <akihiko.odaki@...nix.com>, Jonathan Corbet <corbet@....net>,
 kvm@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 net-next 0/9] virtio: introduce GSO over UDP tunnel

On 6/24/25 4:09 PM, Paolo Abeni wrote:
> Some virtualized deployments use UDP tunnel pervasively and are impacted
> negatively by the lack of GSO support for such kind of traffic in the
> virtual NIC driver.
> 
> The virtio_net specification recently introduced support for GS over
> UDP tunnel, this series updates the virtio implementation to support
> such a feature.
> 
> Currently the kernel virtio support limits the feature space to 64,
> while the virtio specification allows for a larger number of features.
> Specifically the GSO-over-UDP-tunnel-related virtio features use bits
> 65-69.
> 
> The first four patches in this series rework the virtio and vhost
> feature support to cope with up to 128 bits. The limit is set by
> a define and could be easily raised in future, as needed.
> 
> This implementation choice is aimed at keeping the code churn as
> limited as possible. For the same reason, only the virtio_net driver is
> reworked to leverage the extended feature space; all other
> virtio/vhost drivers are unaffected, but could be upgraded to support
> the extended features space in a later time.
> 
> The last four patches bring in the actual GSO over UDP tunnel support.
> As per specification, some additional fields are introduced into the
> virtio net header to support the new offload. The presence of such
> fields depends on the negotiated features.
> 
> New helpers are introduced to convert the UDP-tunneled skb metadata to
> an extended virtio net header and vice versa. Such helpers are used by
> the tun and virtio_net driver to cope with the newly supported offloads.
> 
> Tested with basic stream transfer with all the possible permutations of
> host kernel/qemu/guest kernel with/without GSO over UDP tunnel support.
> 
> This is also are available in the Git repository at:
> 
> git@...hub.com:pabeni/linux-devel.git virtio_udp_tunnel_24_06_2025
> 
> Ideally both the net-next tree and the vhost tree could pull from the
> above.

As Michael prefers to hide the warning in patch 4/9 and this series in
the current form has now conflicts with the current net-next tree, I
just shared a v7, with a more detailed merge plan in the cover letter.

Thanks,

Paolo