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Bug 799028 - [RFE] Add command line option to enable bmi1 feature on AMD processors
Summary: [RFE] Add command line option to enable bmi1 feature on AMD processors
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: qemu-kvm
Version: 6.3
Hardware: x86_64
OS: Linux
unspecified
medium
Target Milestone: rc
: ---
Assignee: Eduardo Habkost
QA Contact: Virtualization Bugs
URL:
Whiteboard:
Depends On: 843084
Blocks: 797283 833128
TreeView+ depends on / blocked
 
Reported: 2012-03-01 15:48 UTC by Peter Krempa
Modified: 2013-02-21 07:32 UTC (History)
13 users (show)

Fixed In Version:
Doc Type: Enhancement
Doc Text:
Clone Of:
Environment:
Last Closed: 2013-02-21 07:32:37 UTC
Target Upstream Version:
Embargoed:


Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2013:0527 0 normal SHIPPED_LIVE qemu-kvm bug fix and enhancement update 2013-02-20 21:51:08 UTC

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


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