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

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Message-ID: <20080929065557.GB9952@redhat.com>
Date:	Mon, 29 Sep 2008 09:55:57 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Alok Kataria <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>,
	Jeremy Fitzhardinge <jeremy@...p.org>, avi@...hat.com,
	Rusty Russell <rusty@...tcorp.com.au>,
	Zachary Amsden <zach@...are.com>,
	Dan Hecht <dhecht@...are.com>, Jun.Nakajima@...el.Com
Subject: Re: Use CPUID to communicate with the hypervisor.

On Fri, Sep 26, 2008 at 04:46:55PM -0700, Alok Kataria wrote:
> From: Alok N Kataria <akataria@...are.com>
> 
> This patch proposes to use a cpuid interface to detect if we are running on an
> hypervisor.
> The discovery of a hypervisor is determined by bit 31 of CPUID#1_ECX, which is
> defined to be "hypervisor present bit". For a VM, the bit is 1, otherwise it is
> set to 0. This bit is not officially documented by either Intel/AMD yet, but
> they plan to do so some time soon, in the meanwhile they have promised to keep
> it reserved for virtualization.
> 
> Also, Intel & AMD have reserved the cpuid levels 0x40000000 - 0x400000FF for
> software use. Hypervisors can use these levels to provide an interface to pass
> information from the hypervisor to the guest. This is similar to how we extract
> information about a physical cpu by using cpuid.
> XEN/KVM are already using the info leaf to get the hypervisor signature.
> 
Can this interface be used to pass variable sized data from a hypervisor
to a gust? ACPI or DMI tables for instance.

--
			Gleb.
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