[rdo-list] Known issue with CentOS 7.3 and qemu-kvm(-ev) 2.6.0

[David Moreau Simard]

Hi,

CentOS 7.3 was released yesterday and a newer version of qemu-kvm-ev
was shipped as part of this release if you have the CentOS
Virtualization SIG repositories enabled.

If you're using RDO >= Newton, you will have this repository enabled.
It was not yet enforced in the Mitaka release so you might or might
not have it, depending on your deployment.
Older releases of OpenStack may also be affected but they are not
proactively tested anymore due to EOL.

There is currently a known issue when using the following
configuration in nova for compute:
==
virt_type=qemu
cpu_mode=host-model
==

This combination will yield in failed attempts at creating instances
and you will see errors like these in nova-compute.log [1] or the
libvirt logs [2].
The problem boils down to libvirt trying to pass a cpu extension that
is unknown to qemu:
==
qemu-kvm: CPU feature arat not found
==

There is a bugzilla [3] for this issue but in the meantime users are
encouraged to work around the issue by setting "cpu_mode=none" if they
are using the qemu (not KVM) hypervisor.
Please note that Nova defaults the 'cpu_mode' parameter to
'host-model' [4] if 'cpu_mode' is not explicitely configured and
'virt_type' is 'qemu' so if you're running into this issue, you will
need to explicitely configure it.

[1]: http://logs.openstack.org/76/409476/4/check/gate-puppet-openstack-integration-4-scenario003-tempest-centos-7/8881991/logs/nova/nova-compute.txt.gz#_2016-12-13_16_39_50_832
[2]: http://logs.openstack.org/76/409476/4/check/gate-puppet-openstack-integration-4-scenario003-tempest-centos-7/8881991/logs/libvirt/qemu/instance-00000001.txt.gz
[3]: https://bugzilla.redhat.com/show_bug.cgi?id=1371617
[4]: http://git.openstack.org/cgit/openstack/nova/tree/nova/virt/libvirt/driver.py?id=146b27f22327f8d60c1017c22ccf18d0e16f1eb7#n3411

David Moreau Simard
Senior Software Engineer | Openstack RDO

dmsimard = [irc, github, twitter]