Live-migration fails with CPU doesn't have compatibility

[Alex Meade]

Live migration in nova does not seem to work as it fails with "CPU doesn't have compatibility" even between hosts with the exact same CPU models. This was introduced recently by the commit below. If I revert Nova to the offending commits parent, the live migration succeeds.

commit 79a0755597f4983367eb0caf4669ffb881b4f720
Author: yunhong jiang <email address hidden>
Date: Fri Feb 6 07:03:45 2015 -0800

    libvirt: fix overly strict CPU model comparison in live migration

    The current libvirt driver migration code checks whether the
    dest host can support the guest, by comparing the source host
    CPU model. This is overly strict, as the guest may well be
    running with a more restrictive CPU model that hides many
    host features. The correct approach is to compare against
    the guest's configured CPU model.

    To achieve the compatibility when migrate instance from old compute
    node which does not provide vcpu_model in instance object, the source
    host's compute info is still provided.

    Co-authored: Daniel P. Berrange <email address hidden>
    Co-authored: Yunhong Jiang <email address hidden>

    Closes-Bug: 1082414

    Change-Id: I65f505fec64c65d2641d2bfd940cde44bcd83a78

nova.conf's libvirt section on both nova nodes is:
[libvirt]
iscsi_use_multipath = True
vif_driver = nova.virt.libvirt.vif.LibvirtGenericVIFDriver
inject_partition = -2
live_migration_uri = qemu+ssh://ameade@%s/system
use_usb_tablet = False
cpu_mode = none
virt_type = kvm

and 'virsh capabilities' on both hosts show the same cpu information as follows:
<cpu>
      <arch>x86_64</arch>
      <model>cpu64-rhel6</model>
      <vendor>Intel</vendor>
      <topology sockets='2' cores='1' threads='1'/>
      <feature name='hypervisor'/>
      <feature name='popcnt'/>
      <feature name='vmx'/>
    </cpu>

[Vladik Romanovsky (vladik-romanovsky)]

Could you please add nova logs, so we could look into it?

[Sean Severson (sseverson)]

This issue was brought up in an existing bug:

https://bugs.launchpad.net/nova/+bug/1082414

There is already a fix under review (currently with a -1) which does work:

https://review.openstack.org/#/c/161944/