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Bug 1309102

Summary:	CPU stepping value different in the same VM when started on different hosts, even if baseline is set via libvirt or RHEV
Product:	Red Hat Enterprise Linux 7	Reporter:	Dan Yasny <dyasny>
Component:	qemu-kvm-rhev	Assignee:	Eduardo Habkost <ehabkost>
Status:	CLOSED INSUFFICIENT_DATA	QA Contact:	Virtualization Bugs <virt-bugs>
Severity:	low	Docs Contact:
Priority:	medium
Version:	7.2	CC:	chayang, dgilbert, dyasny, ehabkost, hhuang, huding, jdenemar, juzhang, knoel, mkalinin, pbonzini, virt-maint, xfu, zhguo
Target Milestone:	rc
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2016-04-28 18:50:12 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:

Description Dan Yasny 2016-02-16 20:29:05 UTC

Description of problem:
When starting a VM on different hosts, inside the VM, the CPU stepping value is different

This can interfere with some software that expects the hardware profile to remain static.

Version-Release number of selected component (if applicable):
[root@hv01 ~]# rpm -qa |grep qemu
qemu-img-rhev-2.1.2-23.el7_1.9.x86_64
qemu-kvm-rhev-2.1.2-23.el7_1.9.x86_64
libvirt-daemon-driver-qemu-1.2.8-16.el7_1.4.x86_64
qemu-kvm-common-rhev-2.1.2-23.el7_1.9.x86_64
qemu-kvm-tools-rhev-2.1.2-23.el7_1.9.x86_64
ipxe-roms-qemu-20130517-6.gitc4bce43.el7.noarch


How reproducible:
always

Steps to Reproduce:
1. start a Windows VM on one host
2. get a CPU-z dump
3. restart the VM on a different host with different CPU (both hosts set to same baseline CPU model, e.g. nehalem)
4. check the CPU-z dump again

Actual results:
different stepping values visible

Expected results:
should be exactly the same

Additional info:

This is a minor issue so far, opening as per request from the virt team. 

Support ticket should be #01584470

Comment 8 Eduardo Habkost 2016-02-17 20:36:07 UTC

(In reply to Dan Yasny from comment #0)
> Steps to Reproduce:
> 1. start a Windows VM on one host
> 2. get a CPU-z dump
> 3. restart the VM on a different host with different CPU (both hosts set to
> same baseline CPU model, e.g. nehalem)
> 4. check the CPU-z dump again
> 
> Actual results:
> different stepping values visible

This description does not match what we see on the CPU-Z dumps. The CPUID stepping field is kept exactly the same. The only CPUID change seen on the two logs is at CPUID[0x80000008].