Re: [PATCH v7 00/14] virtio: introduce support for GSO over UDP tunnel

[Paolo Abeni <pabeni@redhat.com>]

Hi Michael,

On Mon, Sep 22, 2025 at 10:21 PM Paolo Abeni <pabeni@redhat.com> 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 GSO over
> UDP tunnel, and the kernel side of the implementation has been merged
> into the net-next tree; this series updates the virtio implementation to
> support such a feature.
>
> Currently the qemu virtio support limits the feature space to 64 bits,
> 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 larger part of this series (patches 4-12) actually deals with
> extending the features space.
>
> The extended features are carried by fixed size uint64_t arrays,
> bringing the current maximum features number to 128.
>
> The patches use some syntactic sugar to try to minimize the otherwise
> very large code churn. Specifically the extended features are boundled
> in an union with 'legacy' features definition, allowing no changes in
> the virtio devices not needing the extended features set.
>
> The actual offload implementation is in patches 13 and 14 and boils down
> to propagating the new offload to the tun devices and the vhost backend.
>
> Patch 1 is a small pre-req refactor that ideally could enter the
> tree separately; it's presented here in the same series to help
> reviewers more easily getting the full picture, patch 2 updates to
> linux headers update script to deal with annotations recently introduce
> in the kernel and patch 3 is a needed linux headers update.
>
> Tested with basic stream transfer with all the possible permutations of
> host kernel/qemu/guest kernel with/without GSO over UDP tunnel support,
> vs snapshots creation and restore and vs migration.
>
> The new features are disabled by default to avoid compatibilty issues.
> They could be enabled with a later patch, together with the related
> compatiblity entries.

I thing this revision should address your feedback, please LMK
otherwise. I'll follow-up with the FEATURE_ENTRY() macro cleanup as soon
as this will get merged!

Thanks,

Paolo