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

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Message-ID: <51EF7CFB.8030104@redhat.com>
Date:	Wed, 24 Jul 2013 09:06:35 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Jason Wang <jasowang@...hat.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	KY Srinivasan <kys@...rosoft.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

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.

Paolo
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