Re: [PATCH v2] microvm: do not use the lastest cpu version

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Mar 18, 2025 at 12:01:44PM +0100, Paolo Bonzini wrote:
> On 2/20/25 07:53, Ani Sinha wrote:
> > commit 0788a56bd1ae3 ("i386: Make unversioned CPU models be aliases")
> > introduced 'default_cpu_version' for PCMachineClass. This created three
> > categories of CPU models:
> >   - Most unversioned CPU models would use version 1 by default.
> >   - For machines 4.0.1 and older that do not support cpu model aliases, a
> >     special default_cpu_version value of CPU_VERSION_LEGACY is used.
> >   - It was thought that future machines would use the latest value of cpu
> >     versions corresponding to default_cpu_version value of
> >     CPU_VERSION_LATEST [1].
> > 
> > All pc machines still use the default cpu version of 1 for
> > unversioned cpu models. CPU_VERSION_LATEST is a moving target and
> > changes with time.
> 
> Personally I believe this is a problem and I'd rather use CPU_VERSION_LATEST
> for the unversioned pc and q35 models, just like microvm does.

I don't object.

> Unversioned models change the hardware properties and there's no reason for
> CPU properties to be treated differently.  Unversioned models are exactly
> for when you are okay with a moving target.
> 
> And independent of this, microvm could start having versioned variants, so
> that pc and q35 work the same way.
> 
> Paolo
>