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

[KY Srinivasan]

> -----Original Message-----
> From: H. Peter Anvin [mailto:hpa@xxxxxxxxx]
> Sent: Tuesday, July 23, 2013 10:48 AM
> To: KY Srinivasan
> Cc: Jason Wang; tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; x86@xxxxxxxxxx;
> gleb@xxxxxxxxxx; pbonzini@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> 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  



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