Re: [PATCH] target-i386: add feature flags for CPUID[EAX=0xd,ECX=1]

[Paolo Bonzini <pbonzini@redhat.com>]

On 25/11/2014 21:02, Paolo Bonzini wrote:
> > > +static const char *cpuid_xsave_feature_name[] = {
> > > +    "xsaveopt", "xsavec", "xgetbv1", "xsaves",
> > 
> > None of the above features introduce any new state that might need to be
> > migrated, or will require other changes in QEMU to work, right?
> > 
> > It looks like they don't introduce any extra state, but if they do, they
> > need to be added to unmigratable_flags until migration support is
> > implemented.
> > 
> > If they require other QEMU changes, it would be nice if KVM reported
> > them using KVM_CHECK_EXTENSION instead of GET_SUPPORTED_CPUID, so it
> > wouldn't break "-cpu host".
> 
> No, they don't.

Actually, xsaves does but I don't think KVM_CHECK_EXTENSION is right.
It's just another MSR, and we haven't used KVM_CHECK_EXTENSION for new
MSRs and new XSAVE areas (last example: avx512).

Since no hardware really exists for it, and KVM does not support it
anyway, I think it's simplest to leave xsaves out for now.  Is this right?

Paolo