Re: [Qemu-devel] [RFC 00/28] s390x CPU models: exposing features

[David Hildenbrand <dahi@linux.vnet.ibm.com>]

> (CCing libvirt people)
> 
> On Tue, Jun 21, 2016 at 03:02:05PM +0200, David Hildenbrand wrote:
> > This is our second attempt to implement CPU models for s390x. We realized
> > that we also want to have features exposed via the CPU model. While doing
> > that we realized that we want to have a better interface for libvirt.  
> 
> Before getting into the details, I would like to clarify how the
> following could be accomplished using the new commands:
> 
> Example:
> 
> 1) User configures libvirt with:
>    <cpu match='exact'>
>        <model fallback='forbid'>Westmere</model>
>        <feature policy='require' name='aes'/>
>    </cpu>
> 2) libvirt will translate that to:
>    "-cpu Westmere,+aes" or "-cpu Westmere,aes=on"
> 3) libvirt wants to know if "-cpu Westmere,aes=on" is usable in
>    the current host, before trying to start the VM.
> 
> How exactly would this be done using the new commands?

Hi Eduardo,

thanks for having a look - highly appreciated that you actually map this
to libvirt requirements!

That would map to a compare operation between "host" and "Westmere,aes=on".

Host could at that point already be expanded by libvirt. Doesn't matter at that
point.

If the result is "identica"l or "superset", it is runnable. If the result is
"subset" or "incompatible", details about the responsible properties is
indicated. (I actually took that idea from your patch for indicating
runnability).

Thanks!

David