Re: [PATCH] KVM: x86: work around QEMU issue with synthetic CPUID leaves

[Maxim Levitsky <mlevitsk@redhat.com>]

On Sun, 2022-05-01 at 19:37 +0200, Paolo Bonzini wrote:
> On 5/1/22 13:16, Maxim Levitsky wrote:
> > > +		 * However, only do it if the host has CPUID leaf 0x8000001d.
> > > +		 * QEMU thinks that it can query the host blindly for that
> > > +		 * CPUID leaf if KVM reports that it supports 0x8000001d or
> > > +		 * above.  The processor merrily returns values from the
> > > +		 * highest Intel leaf which QEMU tries to use as the guest's
> > > +		 * 0x8000001d.  Even worse, this can result in an infinite
> > > +		 * loop if said highest leaf has no subleaves indexed by ECX.
> > 
> > Very small nitpick: It might be useful to add a note that qemu does this only for the
> > leaf 0x8000001d.
> 
> Yes, it's there: "QEMU thinks that it can query the host blindly for 
> that CPUID leaf", "that" is 0x8000001d in the previous sentence.

Yes I see it, but it doesn't state that qemu doesn't do this to other leaves in the affected range.

I had to check the qemu source to verify this to be sure that checking for 0x8000001d
is enough.

Just a tiny minor nitpick though.

Best regards,
	Maxim Levitsky

> 
> Paolo
>