Bug 799028

Summary:	[RFE] Add command line option to enable bmi1 feature on AMD processors
Product:	Red Hat Enterprise Linux 6	Reporter:	Peter Krempa <pkrempa>
Component:	qemu-kvm	Assignee:	Eduardo Habkost <ehabkost>
Status:	CLOSED ERRATA	QA Contact:	Virtualization Bugs <virt-bugs>
Severity:	medium	Docs Contact:
Priority:	unspecified
Version:	6.3	CC:	acathrow, areis, bsarathy, dallan, ehabkost, emcnabb, juzhang, michen, minovotn, mkenneth, tburke, virt-maint, xfu
Target Milestone:	rc	Keywords:	FutureFeature, TestOnly
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Enhancement
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2013-02-21 07:32:37 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Bug Depends On:	843084
Bug Blocks:	797283, 833128

Description Peter Krempa 2012-03-01 15:48:19 UTC

Description of problem:
The bmi1 support flag is forwarded to the guest OS only if "-cpu host" is used. There is no option to enable exposing this functionality with other (compatible) cpu models. 

When using qemu-kvm managed by libvirt, there's no possibility to use this feature with reasonable configurations. (Host processor passthrough cannot be used easily with migration)

Version-Release number of selected component (if applicable):
qemu-kvm-0.12.1.2-2.235.el6

Steps to Check:
# qemu-kvm -cpu Opteron_G3,+bmi1
CPU feature bmi1 not found

Actual results:
Feature BMI1 cannot be exposed to guest OS without using "-cpu host".

Expected results:
Feature bmi1 can be enabled and exposed to guests using eg "-cpu OpteronG3,+bmi1...".

Additional info:
A option should be added that enables passing through CPUID fn. 0x00000007 reg EBX bit. 3 to the guest OS on compatible processors.

Comment 2 juzhang 2012-03-05 02:27:34 UTC

Hi,Peter

   About bmi1 flag,would you please tell qe which amd platforms(host) includes this flag? thanks

Comment 3 Peter Krempa 2012-03-05 09:56:59 UTC

Hi Junyi,
the bmi1 flag is exposed on hosts that support the new bit manipulation instructions. This feature is included in the new Piledriver architecture from AMD.

Comment 5 juzhang 2012-03-06 01:39:15 UTC

Thanks peter,according to comment3 and comment4,set qa_ack+

Comment 13 FuXiangChun 2012-11-26 09:36:56 UTC

verify this bug with qemu-kvm-0.12.1.2-2.334.el6.x86_64 and kernel 2.6.32-339.el6.x86_64

steps to verify:
1.boot rhel6.4 guest with -cpu Opteron_G3,+bmi1 on Seoul host
2.check flag bmil inside guest. 

result:
'bmil' flag is exposed to guest

so according to expected results in description, this bug is fixed.

Comment 15 errata-xmlrpc 2013-02-21 07:32:37 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.

http://rhn.redhat.com/errata/RHBA-2013-0527.html