Bug 799028 - [RFE] Add command line option to enable bmi1 feature on AMD processors
[RFE] Add command line option to enable bmi1 feature on AMD processors
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: qemu-kvm (Show other bugs)
x86_64 Linux
unspecified Severity medium
: rc
: ---
Assigned To: Eduardo Habkost
Virtualization Bugs
: FutureFeature, TestOnly
Depends On: 843084
Blocks: 797283 833128
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Reported: 2012-03-01 10:48 EST by Peter Krempa
Modified: 2013-02-21 02:32 EST (History)
13 users (show)

See Also:
Fixed In Version:
Doc Type: Enhancement
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2013-02-21 02:32:37 EST
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
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oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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Description Peter Krempa 2012-03-01 10:48:19 EST
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):

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 2012-03-04 21:27:34 EST

   About bmi1 flag,would you please tell qe which amd platforms(host) includes this flag? thanks
Comment 3 Peter Krempa 2012-03-05 04:56:59 EST
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 2012-03-05 20:39:15 EST
Thanks peter,according to comment3 and comment4,set qa_ack+
Comment 13 FuXiangChun 2012-11-26 04:36:56 EST
verify this bug with qemu-kvm- 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. 

'bmil' flag is exposed to guest

so according to expected results in description, this bug is fixed.
Comment 15 errata-xmlrpc 2013-02-21 02:32:37 EST
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.


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