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

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Message-ID: <c7e8bcb7eb25448497107b1a94463f27@SN2PR03MB061.namprd03.prod.outlook.com>
Date:	Tue, 23 Jul 2013 22:42:18 +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 2:46 PM
> 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 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


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