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

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Message-ID: <ddd4ff1d4b124faeb18e6a0ba8ae2128@BLUPR03MB050.namprd03.prod.outlook.com>
Date:	Wed, 24 Jul 2013 14:01:26 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Jason Wang <jasowang@...hat.com>
CC:	"H. Peter Anvin" <hpa@...or.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>,
	"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: Paolo Bonzini [mailto:paolo.bonzini@...il.com] On Behalf Of Paolo
> Bonzini
> Sent: Wednesday, July 24, 2013 3:07 AM
> To: Jason Wang
> Cc: H. Peter Anvin; KY Srinivasan; tglx@...utronix.de; mingo@...hat.com;
> x86@...nel.org; gleb@...hat.com; kvm@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Subject: Re: [PATCH 4/4] x86: properly handle kvm emulation of hyperv
> 
> Il 24/07/2013 08:54, Jason Wang ha scritto:
> > On 07/24/2013 12:48 PM, H. Peter Anvin wrote:
> >> On 07/23/2013 09:37 PM, Jason Wang wrote:
> >>> On 07/23/2013 10:48 PM, H. Peter Anvin wrote:
> >>>> 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...
> >>>>
> >>>> 	-hpa
> >>>>
> >>> How about simply does a reverse loop from 0x40010000 to 0x40010000?
> >>>
> >> Not all systems like being poked too far into hyperspace.  Just remember
> >> the last match and walk the list.
> >>
> >> 	-hpa
> >>
> >
> > Ok, but it raises a question - how to know it was the 'last' match
> > without knowing all signatures of other hyper-visor?
> 
> You can return a "priority" value from the .detect function.  The
> priority value can simply be the CPUID leaf where the signature was
> found (or a low value such as 1 if detection was done with DMI).
> 
> Then you can pick the hypervisor with the highest priority instead of
> hard-coding the order.

I like this idea; this allows some guest level control that is what we want
when we have hypervisors emulating each other.


Regards,

K. Y 
> 
> Paolo
> 
> 



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