Re: [PATCH v7 net-next 0/9] virtio: introduce GSO over UDP tunnel

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

On Tue, Jul 08, 2025 at 09:08:56AM +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 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.
> ---
> WRT the merge plan, this is also are available in the Git repository at
> [1]:
> 
> git@github.com:pabeni/linux-devel.git virtio_udp_tunnel_07_07_2025
> 
> The first 5 patches in this series, that is, the virtio features
> extension bits are also available at [2]:
> 
> git@github.com:pabeni/linux-devel.git virtio_features_extension_07_07_2025
> 
> Ideally the virtio features extension bit should go via the virtio tree
> and the virtio_net/tun patches via the net-next tree. The latter have
> a dependency in the first and will cause conflicts if merged via the
> virtio tree, both when applied and at merge window time - inside Linus
> tree.
> 
> To avoid such conflicts and duplicate commits I think the net-next
> could pull from [1], while the virtio tree could pull from [2].

Or I could just merge all of this in my tree, if that's ok
with others?

Willem/Jason ok with you?





> ---
> v6 -> v7:
>   - avoid warning in csky build
>   - rebased
> v6: https://lore.kernel.org/netdev/cover.1750753211.git.pabeni@redhat.com/
> 
> v5 -> v6:
>   - fix integer overflow in patch 4/9
> v5: https://lore.kernel.org/netdev/cover.1750436464.git.pabeni@redhat.com/
> 
> v4 -> v5:
>   - added new patch 1/9 to avoid kdoc issues
>   - encapsulate guest features guessing in new tap helper
>   - cleaned-up SET_FEATURES_ARRAY
>   - a few checkpatch fixes
> v4: https://lore.kernel.org/netdev/cover.1750176076.git.pabeni@redhat.com/
> 
> v3 -> v4:
>   - vnet sockopt cleanup
>   - fixed offset for UDP-tunnel related field
>   - use dev->features instead of flags
> v3: https://lore.kernel.org/netdev/cover.1749210083.git.pabeni@redhat.com/
> 
> v2 -> v3:
>   - uint128_t -> u64[2]
>   - dropped related ifdef
>   - define and use vnet_hdr with tunnel layouts
> v2: https://lore.kernel.org/netdev/cover.1748614223.git.pabeni@redhat.com/
> 
> v1 -> v2:
>   - fix build failures
>   - many comment clarification
>   - changed the vhost_net ioctl API
>   - fixed some hdr <> skb helper bugs
> v1: https://lore.kernel.org/netdev/cover.1747822866.git.pabeni@redhat.com/
> 
> Paolo Abeni (9):
>   scripts/kernel_doc.py: properly handle VIRTIO_DECLARE_FEATURES
>   virtio: introduce extended features
>   virtio_pci_modern: allow 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                      |  58 ++++++--
>  drivers/net/tun_vnet.h                 | 101 +++++++++++--
>  drivers/net/virtio_net.c               | 110 +++++++++++---
>  drivers/vhost/net.c                    |  95 +++++++++---
>  drivers/vhost/vhost.c                  |   2 +-
>  drivers/vhost/vhost.h                  |   4 +-
>  drivers/virtio/virtio.c                |  43 +++---
>  drivers/virtio/virtio_debug.c          |  27 ++--
>  drivers/virtio/virtio_pci_modern.c     |  10 +-
>  drivers/virtio/virtio_pci_modern_dev.c |  69 +++++----
>  include/linux/virtio.h                 |   9 +-
>  include/linux/virtio_config.h          |  43 +++---
>  include/linux/virtio_features.h        |  88 +++++++++++
>  include/linux/virtio_net.h             | 197 ++++++++++++++++++++++++-
>  include/linux/virtio_pci_modern.h      |  43 +++++-
>  include/uapi/linux/if_tun.h            |   9 ++
>  include/uapi/linux/vhost.h             |   7 +
>  include/uapi/linux/vhost_types.h       |   5 +
>  include/uapi/linux/virtio_net.h        |  33 +++++
>  scripts/lib/kdoc/kdoc_parser.py        |   1 +
>  20 files changed, 790 insertions(+), 164 deletions(-)
>  create mode 100644 include/linux/virtio_features.h
> 
> -- 
> 2.49.0