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Date: Tue, 30 Sep 2008 12:16:18 +0300
From: Avi Kivity <avi@redhat.com>
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To: "Nakajima, Jun" <jun.nakajima@intel.com>
CC: Gleb Natapov <gleb@redhat.com>, Alok Kataria <akataria@vmware.com>,
       Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>,
       Thomas Gleixner <tglx@linutronix.de>,
       LKML <linux-kernel@vger.kernel.org>,
       the arch/x86 maintainers <x86@kernel.org>,
       Jeremy Fitzhardinge <jeremy@goop.org>,
       Rusty Russell <rusty@rustcorp.com.au>, Zachary Amsden <zach@vmware.com>,
       Dan Hecht <dhecht@vmware.com>
Subject: Re: Use CPUID to communicate with the hypervisor.
References: <1222472815.29886.43.camel@alok-dev1> <20080929065557.GB9952@redhat.com> <48E085B3.1080507@redhat.com> <0B53E02A2965CE4F9ADB38B34501A3A15726DBE3@orsmsx505.amr.corp.intel.com>
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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.