Comment 5 for bug 1903822

In fact, I believe using `virsh capabilities` to compare cpu features is incorrect, at least for host-model

* libvirt will use qemu qmp command `query-cpu-model-expansion` to retrieve a list of cpu features and whether it is supported
* some features like `monitor` which is not implemented will not be required and thus not affect live migration at all
* even if cpuid is different for two hosts, it is not implying live migration is forbid, because it is dependent on whether qemu implements it or not
* also, some features like `invtsc` or `hypervisor` is not part of any common cpu but provides by qemu will also actually be required in the live domain

and of course I am no expert in libvirt or qemu, so apologize in advance if my understanding is incorrect...

besides, right now if live migration from A to B succeeds, live migration back (no stop/reboot in between) should also work but for the current nova code it is not.