[libvirt] Incompatible CPU after upgrading qemu

[Jim Fehlig]

On 04/18/2017 12:35 AM, Jiri Denemark wrote:
> On Thu, Apr 13, 2017 at 16:11:26 -0600, Jim Fehlig wrote:
>> Hi All,
>>
>> I've been doing some upgrade testing and noticed a problem starting some
>> existing VMs after upgrading qemu from 2.6 to 2.9 on one of my AMD machines.
>> Using libvirt 3.2.0 and qemu 2.6, I have no problems starting a VM with the
>> following machine/CPU config
>>
>>   <os>
>>     <type arch='x86_64' machine='pc-i440fx-2.6'>hvm</type>
>>     <boot dev='hd'/>
>>   </os>
>>    <cpu mode='custom' match='exact'>
>>     <model fallback='allow'>Opteron_G4</model>
>>   </cpu>
>>
>> After upgrading qemu to 2.9 the VM fails to start with
>>
>> error: the CPU is incompatible with host CPU: Host CPU does not provide required
>> features: svm
>>
>> I see that qemu commit 75d373ef disables SVM in KVM mode, but that change was
>> made quite some time ago and pertains to all machine types > pc-i440fx-2.2.
>> Perhaps the problem was revealed by Jiri's recent libvirt changes to detect host
>> CPU model by asking qemu?
>>
>> My knee-jerk reaction is to remove 'svm' from Opteron CPUs in cpu_map.xml, but
>> I'm far from the expert on the evolving CPU code in libvirt, so asking the
>> experts here for some guidance.
>
> This issue should be fixed by "qemu: More CPU enhancements and fixes"
> series [1], specifically patch 9/9. See the commit message for more
> details.
>
> [1] https://www.redhat.com/archives/libvir-list/2017-April/msg00710.html

Thanks. Although I haven't reviewed the series, I did test it and indeed it 
fixes the issue.

Regards,
Jim