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

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Message-ID: <48E1EE62.3070608@redhat.com>
Date:	Tue, 30 Sep 2008 12:16:18 +0300
From:	Avi Kivity <avi@...hat.com>
To:	"Nakajima, Jun" <jun.nakajima@...el.com>
CC:	Gleb Natapov <gleb@...hat.com>, Alok Kataria <akataria@...are.com>,
	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>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Zachary Amsden <zach@...are.com>, Dan Hecht <dhecht@...are.com>
Subject: Re: Use CPUID to communicate with the hypervisor.

Nakajima, Jun wrote:
> On 9/29/2008 12:37:23 AM, Avi Kivity wrote:
>   
>> Gleb Natapov wrote:
>>     
>>> Can this interface be used to pass variable sized data from a
>>> hypervisor to a gust? ACPI or DMI tables for instance.
>>>
>>>       
>> In theory it can, but it would be a bad idea.  cpuid is best used to
>> communicate cpu features; ACPI and DMI are (mostly) system features.
>>     
>
> Also, we have reserved the MSRs from 0x40000000 - 0x400000FF for software use. We could use such MSRs, but what's the benefits of using those when ACPI already defined the detection mechanism?
>
>   

Features that the guest needs to enable very early on, before ACPI is 
up.  I don't think there are many of those.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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