Re: [PATCH v3] target/i386: Fix CPUID encoding of Fn8000001E_ECX

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, May 10, 2024 at 11:05:44AM +0300, Michael Tokarev wrote:
> 09.05.2024 17:11, Daniel P. Berrangé wrote:
> > On Thu, May 09, 2024 at 04:54:16PM +0300, Michael Tokarev wrote:
> > > 03.05.2024 20:46, Babu Moger wrote:
> 
> > > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > > > index 08c7de416f..46235466d7 100644
> > > > --- a/hw/i386/pc.c
> > > > +++ b/hw/i386/pc.c
> > > > @@ -81,6 +81,7 @@
> > > >    GlobalProperty pc_compat_9_0[] = {
> > > >        { TYPE_X86_CPU, "guest-phys-bits", "0" },
> > > >        { "sev-guest", "legacy-vm-type", "true" },
> > > > +    { TYPE_X86_CPU, "legacy-multi-node", "on" },
> > > >    };
> > > 
> > > Should this legacy-multi-node property be added to previous
> > > machine types when applying to stable?  How about stable-8.2
> > > and stable-7.2?
> > 
> > machine types are considered to express a fixed guest ABI
> > once part of a QEMU release. Given that we should not be
> > changing existing machine types in stable branches.
> 
> Yes, I understand this, and this is exactly why I asked.
> The change in question has been Cc'ed to stable.  And I'm
> trying to understand what should I do with it :)
> 
> > In theory we could create new "bug fix" machine types in stable
> > branches. To support live migration, we would then need to also
> > add those same stable branch "bug fix" machine type versions in
> > all future QEMU versions. This is generally not worth the hassle
> > of exploding the number of machine types.
> > 
> > If you backport the patch, minus the machine type, then users
> > can still get the fix but they'll need to manually set the
> > property to enable it.
> 
> I don't think this makes big sense.  But maybe for someone who
> actually hits this issue such backport will let to fix it.
> Hence, again, I'm asking if it really a good idea to pick this
> up for stable (any version of, - currently there are 2 active
> series, 7.2, 8.2 and 9.0).

Hmm, the description says

  "Observed the following failure while booting the SEV-SNP guest"

and yet the patches for SEV-SNP are *not* merged in QEMU yet. So this
does not look relevant for stable unless I'm missing something.

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|