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

[Jason Wang]

On Thu, Jun 16, 2022 at 7:59 PM Andrew Melnichenko <andrew@xxxxxxxxxx> wrote:
>
> Hi, Jason
> Apparently, your patch should work.
> For now, I have an issue where segmentation between two guests on one
> host still occurs.
> Neither previous "hack" nor your patch helps.
> Now I'm looking what the issue may be.
> If you have some suggestions on where may I look, it would be helpful, thanks!

I think maybe it's worth tracking which function did the segmentation.

Thanks

>
> On Thu, May 26, 2022 at 3:18 PM Andrew Melnichenko <andrew@xxxxxxxxxx> wrote:
> >
> > I'll check it, thank you!
> >
> > On Thu, May 26, 2022 at 9:56 AM Jason Wang <jasowang@xxxxxxxxxx> wrote:
> > >
> > > On Tue, May 24, 2022 at 7:07 PM Andrew Melnichenko <andrew@xxxxxxxxxx> 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@xxxxxxxxxx> wrote:
> > > > >
> > > > > On Thu, May 12, 2022 at 7:33 PM Andrew Melnychenko <andrew@xxxxxxxxxx> 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
> > > > > >
> > > > >
> > > >
>