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

KY Srinivasan
2013-07-23T17:45:04Z

> -----Original Message-----
> From: H. Peter Anvin [mailto:hpa@zytor.com]
> Sent: Tuesday, July 23, 2013 10:48 AM
> 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 06:55 AM, KY Srinivasan wrote:
> >
> > This strategy of hypervisor detection based on some detection order IMHO is
> not
> > a robust detection strategy. The current scheme works since the only
> hypervisor emulated
> > (by other hypervisors happens to be Hyper-V). What if this were to change.
> >
>
> 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.

Regards,

K. Y