[libvirt] Incompatible CPU after upgrading qemu

[Jiri Denemark]

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

Jirka