linux-kernel - Re: Use CPUID to communicate with the hypervisor.

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Date:	Sat, 27 Sep 2008 22:01:01 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	akataria@...are.com
CC:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	"avi@...hat.com" <avi@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Zach Amsden <zach@...are.com>,
	Daniel Hecht <dhecht@...are.com>,
	"Jun.Nakajima@...el.Com" <Jun.Nakajima@...el.Com>,
	Tim Deegan <Tim.Deegan@...rix.com>
Subject: Re: Use CPUID to communicate with the hypervisor.

Alok Kataria wrote:
>> I think there's a move towards doing a scan for a signature, such as
>> checking every 16 leaves after 0x40000000 for "a while" looking for
>> interesting signatures, so that a hypervisor can support multiple ABIs
>> at once.  Given this, it would be better to define a "Generic Hypervisor
>> ABI" signature, and put all the related leaves together.
>>     
>
> Hmm interesting, do you have any pointers to this ?
>   

No.  I think I saw a passing reference from Tim Deegan to it, but I
couldn't find it again when I looked.

> As far as live migration, for full-virt, we think that it should happen
> invisibly to the guest.  So even if we move to a host with different TSC
> frequency it should be the job of the hypervisor to still emulate the
> old frequency. 
>   

Can the tsc be emulated without a performance hit, or does it trap into
the hypervisor?

    J
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