On Tue, Nov 7, 2017 at 5:02 PM, Michal Kubecek <mkube...@suse.cz> wrote: > Hello, > > I just received this bug report: > > https://bugzilla.suse.com/show_bug.cgi?id=1066757 > > The reporter runs a live migration of a kvm guest from a host with > kernel supporting UFO (openSUSE 42.2 or 42.3, based on 4.4) to a host > with kernel with UFO support removed (SLE15 or openSUSE 15.0 pre-release > which is based on 4.12 but has the UFO removal series backported). > > The migration fails with > > kvm: virtio-net: saved image requires TUN_F_UFO support > > because the guest image has a virtio_net device with UFO enabled which > requires TUN_F_UFO on the corresponding host tun device but that is no > longer available on the target host. > > This kind of problem already happened once: > > https://www.spinics.net/lists/netdev/msg443821.html > > At that time, commit 3d0ad09412ff ("drivers/net: Disable UFO through > virtio") was reverted once the issue it worked around was resolved in > a different way. > > I didn't have time to think it through yet but perhaps we could allow > setting TUN_F_UFO and ignore its value.
If the feature is enabled guests may try to send UFO packets, which the host is no longer able to fragment. virtio_net_hdr_to_skb will drop the packets immediately based on gso_type and tun_get_user will return EINVAL. Still, perhaps that's preferable as migration will succeed and most guests won't ever try to send those packets in the first place. > This is not time critical for SLE15 / openSUSE 15.0 which are still at > early beta stage but 4.14 final is close and once it's out, more users > are going to hit this. > > Michal Kubecek >
