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

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Message-ID: <e31a95e22bbc4c8dbbf76f88b8c90581@SN2PR03MB061.namprd03.prod.outlook.com>
Date:	Tue, 23 Jul 2013 17:45:04 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Jason Wang <jasowang@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"gleb@...hat.com" <gleb@...hat.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 4/4] x86: properly handle kvm emulation of hyperv



> -----Original Message-----
> From: H. Peter Anvin [mailto:hpa@...or.com]
> Sent: Tuesday, July 23, 2013 10:48 AM
> To: KY Srinivasan
> Cc: Jason Wang; tglx@...utronix.de; mingo@...hat.com; x86@...nel.org;
> gleb@...hat.com; pbonzini@...hat.com; kvm@...r.kernel.org; linux-
> kernel@...r.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  



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