On Tue, May 24, 2022 at 7:07 PM Andrew Melnichenko <andrew@daynix.com> wrote:
>
> Hi all,
>
> The issue is that host segments packets between guests on the same host.
> Tests show that it happens because SKB_GSO_DODGY skb offload in
> virtio_net_hdr_from_skb().
> To do segmentation you need to remove SKB_GSO_DODGY or add SKB_GSO_PARTIAL
> The solution with DODGY/PARTIAL offload looks like a dirty hack, so
> for now, I've lived it as it is for further investigation.

Ok, I managed to find the previous discussion. It looks to me the
reason is that __udp_gso_segment will segment dodgy packets
unconditionally.

I wonder if the attached patch works? (compile test only).

Thanks

>
>
> On Tue, May 17, 2022 at 9:32 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Thu, May 12, 2022 at 7:33 PM Andrew Melnychenko <andrew@daynix.com> wrote:
> > >
> > > Added new offloads for TUN devices TUN_F_USO4 and TUN_F_USO6.
> > > Technically they enable NETIF_F_GSO_UDP_L4
> > > (and only if USO4 & USO6 are set simultaneously).
> > > It allows to transmission of large UDP packets.
> > >
> > > Different features USO4 and USO6 are required for qemu where Windows guests can
> > > enable disable USO receives for IPv4 and IPv6 separately.
> > > On the other side, Linux can't really differentiate USO4 and USO6, for now.
> > > For now, to enable USO for TUN it requires enabling USO4 and USO6 together.
> > > In the future, there would be a mechanism to control UDP_L4 GSO separately.
> > >
> > > Test it WIP Qemu https://github.com/daynix/qemu/tree/Dev_USOv2
> > >
> > > New types for VirtioNet already on mailing:
> > > https://lists.oasis-open.org/archives/virtio-comment/202110/msg00010.html
> > >
> > > Also, there is a known issue with transmitting packages between two guests.
> >
> > Could you explain this more? It looks like a bug. (Or any pointer to
> > the discussion)
> >
> > Thanks
> >
> > > Without hacks with skb's GSO - packages are still segmented on the host's postrouting.
> > >
> > > Andrew (5):
> > >   uapi/linux/if_tun.h: Added new offload types for USO4/6.
> > >   driver/net/tun: Added features for USO.
> > >   uapi/linux/virtio_net.h: Added USO types.
> > >   linux/virtio_net.h: Support USO offload in vnet header.
> > >   drivers/net/virtio_net.c: Added USO support.
> > >
> > >  drivers/net/tap.c               | 10 ++++++++--
> > >  drivers/net/tun.c               |  8 +++++++-
> > >  drivers/net/virtio_net.c        | 19 +++++++++++++++----
> > >  include/linux/virtio_net.h      |  9 +++++++++
> > >  include/uapi/linux/if_tun.h     |  2 ++
> > >  include/uapi/linux/virtio_net.h |  4 ++++
> > >  6 files changed, 45 insertions(+), 7 deletions(-)
> > >
> > > --
> > > 2.35.1
> > >
> >
>