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SubjectRe: [RFC PATCH v2 0/5] TUN/VirtioNet USO features support.
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.


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
> >
>

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