Comment 2 for bug 1783140

Of the listed guests I assume Ubuntu 18.04 has the newest guest Kernel (read virtio drivers).
Several questions to ensure this is right:

1. could you report the kernel version of each of your test guests (assuming 4.4 and 4.15 for Ubuntu, but the exact version would be great to know)

2. it would be great to know if one of the newer qemu versions that already exist fix the virtio handling of this case. So once you recreated your case could you upgrade through the Ubuntu Cloud Archive provided versions and let us know if some of them work (and if so which ones exactly).
That might help a lot to track down a potentially existing virtio fix.
Just one by one upgrade the newer versions from [1] on source and target host.
Then shutdown and re-start your guest on the migration source and then migrate again.

3. #2 above changed qemu, the other element we might change is that you use the 4.15 based HWE kernel in a 16.04 guest - would that then fail just as the 18.04 guest does?

In general, I wonder what on this should be Power specific since it should after all use the same virtio drivers and host code.
I have seen other similar reports which always ended up as host/guest mismatch of virtio-handling - but never an arch specific one yet.

[1]: https://wiki.ubuntu.com/OpenStack/CloudArchive