RE: [PATCH 4/4] x86: properly handle kvm emulation of hyperv

KY Srinivasan
2013-07-23T22:42:18Z

> -----Original Message-----
> From: H. Peter Anvin [mailto:hpa@zytor.com]
> Sent: Tuesday, July 23, 2013 2:46 PM
> To: KY Srinivasan
> Cc: Jason Wang; tglx@linutronix.de; mingo@redhat.com; x86@kernel.org;
> gleb@redhat.com; pbonzini@redhat.com; kvm@vger.kernel.org; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH 4/4] x86: properly handle kvm emulation of hyperv
>
> On 07/23/2013 10:45 AM, KY Srinivasan wrote:
> >>
> >> One strategy would be to pick the *last* one in the CPUID list, since
> >> the ones before it are logically the one(s) being emulated...
> >
> > Is it always possible to guarantee this ordering. As a hypothetical, what if
> hypervisor A
> > emulates Hypervisor B and Hypervisor B emulates Hypervisor A. In this case we
> cannot
> > have any "order" based detection that can yield "correct" detection. I define
> "correctness"
> > as follows:
> >
> > If a guest can run on both the hypervisors, the guest should detect the true
> native
> > Hypervisor.at
> >
>
> My point was that most hypervisors tend to put the native signature at
> the end of the list starting at 0x40000000, just to deal with naïve
> guests which only look at 0x40000000 and not beyond. So a natural
> convention would be to "use the last entry in the list you know how to
> handle."

Ok; thanks for the clarification.

Regards,

K. Y