Comment # 2 on bug 1066757 from Michal Kube��ek

Just to be sure I understand the scenario correctly: you have a VM image of
a guest system with kernel where virtio_net still supports UFO (and has it
enabled), i.e. anything older than SLE15 / openSUSE-15.0, and do live migration
from a host with e.g 42.3 (SLE12-SP3) kernel to a host running openSUSE-15.0
or SLE15 (Beta 1 or later) kernel. Am I right?

That would indeed be a problem. This happened once already:

  http://www.spinics.net/lists/kvm/msg110142.html

That time, the offending commit was reverted (after the primary issue with
IPv6 fragments it aimed to work around was fixed properly).

In any case, this is something that needs to be discussed in upstream even
if the timing is really unfortunate (4.14 final around the corner and
netconf/netdev conference this week).