Bug 1579691

Summary:	[Deployment][RHOSP-13] Lift the restriction on choices for `cpu_model_extra_flags` config attribute
Product:	Red Hat OpenStack	Reporter:	Rajesh Tailor <ratailor>
Component:	puppet-nova	Assignee:	Rajesh Tailor <ratailor>
Status:	CLOSED ERRATA	QA Contact:	OSP DFG:Compute <osp-dfg-compute>
Severity:	medium	Docs Contact:
Priority:	medium
Version:	13.0 (Queens)	CC:	jjoyce, joflynn, jschluet, lyarwood, nlevinki, nova-maint, ratailor, slinaber, tvignaud
Target Milestone:	z2	Keywords:	Triaged, ZStream
Target Release:	13.0 (Queens)
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	puppet-nova-12.4.0-6.el7ost	Doc Type:	Enhancement
Doc Text:	Nova's libvirt driver now allows the specification of granular CPU feature flags when configuring CPU models. One benefit of this is the alleviation of a performance degradation experienced on guests running with certain Intel-based virtual CPU models after application of the "Meltdown" CVE fixes. This guest performance impact is reduced by exposing the CPU feature flag 'PCID' ("Process-Context ID") to the guest CPU, assuming that the PCID flag is available in the physical hardware itself. This change removes the restriction of having only 'PCID' as the only CPU feature flag and allows for the addition and removal of multiple CPU flags, making way for other use cases. For more information, refer to the documentation of ``[libvirt]/cpu_model_extra_flags`` in ``nova.conf``.	Story Points:	---
Clone Of:	1579681
Clones:	1579693 (view as bug list)		Environment:
Last Closed:	2018-08-29 16:36:37 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1579681, 1579699
Bug Blocks:	1579693, 1579694

Description Rajesh Tailor 2018-05-18 07:07:51 UTC

+++ This bug was initially created as a clone of Bug #1579681 +++

(This bug is a follow-up item to the:
https://bugzilla.redhat.com/show_bug.cgi?id=1547954 -- Deployment RFE: add ability to configure extra CPU flags for named CPU models)

This introduced the Nova configuration attribute
`[libvirt]/cpu_model_extra_flags`, we have restricted the choices to be
only 'PCID' -- to alleviate the immediate guest performance degradation
as a result of applying the "Meltdown" CVE fixes.

Now remove that restriction to allow adding and removing multiple CPU
flags, making way for other use cases.

Use cases:

  - Ability to use 1GB huge pages with Haswell model as one use case for
    extra flags:

        cpu_model=Haswell-noTSX-IBRS 
        cpu_model_extra_flags="pdpe1gb"

  - Nested Virtualization -- an operator can specify the Intel 'vmx' or
    AMD 'svm' flags in the level-1 Nova guest.

Comment 13 Joanne O'Flynn 2018-08-15 08:05:56 UTC

This bug is marked for inclusion in the errata but does not currently contain draft documentation text. To ensure the timely release of this advisory please provide draft documentation text for this bug as soon as possible.

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Comment 15 errata-xmlrpc 2018-08-29 16:36:37 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2018:2574