The patch[*] is already in RHOS-13:
$> git branch --contains 98eb85f
[*] From RHOS-13 branch:
$ git show 98eb85f
Author: Kashyap Chamarthy <email@example.com>
Date: Tue Jan 16 17:56:51 2018 +0100
libvirt: Allow to specify granular CPU feature flags
The recent "Meltdown" CVE fixes have resulted in a critical performance
penalty[*] that will impact every Nova guest with certain CPU models.
I.e. assume you have applied all the "Meltdown" CVE fixes, and performed
a cold reboot (explicit stop & start) of all Nova guests, for the
updates to take effect. Now, if any guests that are booted with certain
named virtual CPU models (e.g. "IvyBridge", "Westmere", etc), then those
guests, will incur noticeable performance degradation[*], while being
protected from the CVE itself.
To alleviate this guest performance impact, it is now important to
specify an obscure Intel CPU feature flag, 'PCID' (Process-Context ID)
-- for the virtual CPU models that don't already include it (more on
this below). To that end, this change will allow Nova to explicitly
specify CPU feature flags via a new configuration attribute,
`cpu_model_extra_flags`, e.g. in `nova.conf`:
According to our records, this should be resolved by openstack-nova-17.0.3-0.20180420001141.el7ost. This build is available now.