linux-kernel - Re: [RFC] CPUID usage for interaction between Hypervisors and Linux.

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Message-ID: <48E3D8A8.604@goop.org>
Date:	Wed, 01 Oct 2008 13:08:08 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Anthony Liguori <anthony@...emonkey.ws>
CC:	akataria@...are.com, kvm@...r.kernel.org,
	the arch/x86 maintainers <x86@...nel.org>,
	Dan Hecht <dhecht@...are.com>,
	LKML <linux-kernel@...r.kernel.org>,
	virtualization@...ts.linux-foundation.org,
	"avi@...hat.com" <avi@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC] CPUID usage for interaction between Hypervisors and Linux.

Anthony Liguori wrote:
> Mmm, cpuid bikeshedding :-)

My shade of blue is better.

>> The space 0x40000000-0x400000ff is reserved for hypervisor usage.
>>
>> This region is divided into 16 16-leaf blocks.  Each block has the 
>> structure:
>>
>> 0x400000x0:
>>     eax: max used leaf within the leaf block (max 0x400000xf)
>
> Why even bother with this?  It doesn't seem necessary in your proposal.

It allows someone to incrementally add things to their block in a fairly 
orderly way.  But more importantly, its the prevailing idiom, and the 
existing and proposed cpuid schemes already do this, so they'd fit in as-is.

    J
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