Re: [PATCH net-next 0/8] virtio: introduce GSO over UDP tunnel

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, May 21, 2025 at 12:32:34PM +0200, 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 GSO 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 arch-dependent:
> only arches with native 128 integer support allow for the wider feature
> space.
> 
> 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.
> 
> A new pair of helpers is 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.
> Sharing somewhat early to collect feedback, especially on the userland
> code.


I like the approach. Some small comments/questions.

> Paolo Abeni (8):
>   virtio: introduce virtio_features_t
>   virtio_pci_modern: allow setting configuring extended features
>   vhost-net: allow configuring extended features
>   virtio_net: add supports for extended offloads
>   net: implement virtio helpers to handle UDP GSO tunneling.
>   virtio_net: enable gso over UDP tunnel support.
>   tun: enable gso over UDP tunnel support.
>   vhost/net: enable gso over UDP tunnel support.
> 
>  drivers/net/tun.c                      |  77 +++++++++--
>  drivers/net/tun_vnet.h                 |  74 +++++++++--
>  drivers/net/virtio_net.c               |  99 ++++++++++++--
>  drivers/vhost/net.c                    |  32 ++++-
>  drivers/vhost/vhost.h                  |   2 +-
>  drivers/virtio/virtio.c                |  12 +-
>  drivers/virtio/virtio_mmio.c           |   4 +-
>  drivers/virtio/virtio_pci_legacy.c     |   2 +-
>  drivers/virtio/virtio_pci_modern.c     |   7 +-
>  drivers/virtio/virtio_pci_modern_dev.c |  44 +++---
>  drivers/virtio/virtio_vdpa.c           |   2 +-
>  include/linux/virtio.h                 |   5 +-
>  include/linux/virtio_config.h          |  22 +--
>  include/linux/virtio_features.h        |  23 ++++
>  include/linux/virtio_net.h             | 177 +++++++++++++++++++++++--
>  include/linux/virtio_pci_modern.h      |  11 +-
>  include/uapi/linux/if_tun.h            |   9 ++
>  include/uapi/linux/vhost.h             |   8 ++
>  include/uapi/linux/virtio_net.h        |  33 +++++
>  19 files changed, 551 insertions(+), 92 deletions(-)
>  create mode 100644 include/linux/virtio_features.h
> 
> -- 
> 2.49.0