linux-kernel - RE: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V

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Message-Id: <510A2D5802000078000BAEAA@nat28.tlf.novell.com>
Date:	Thu, 31 Jan 2013 07:37:44 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"KY Srinivasan" <kys@...rosoft.com>
Cc:	"olaf@...fle.de" <olaf@...fle.de>, "bp@...en8.de" <bp@...en8.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>
Subject: RE: [PATCH 2/3] X86: Add a check to catch Xen emulation of
 Hyper-V

>>> On 30.01.13 at 19:12, KY Srinivasan <kys@...rosoft.com> wrote:
> Presumably, Hyper-V emulation is only to run enlightened Windows. The issue 
> with
> Xen is not that it emulates Hyper-V, but this emulation is turned on while 
> running Linux.
> That is the reason I chose to check for Xen. Would you prefer a DMI check 
> for the Hyper-V
> platform. 

I consider DMI checks to be too fragile here - in particular with
the eventual passing through of host DMI attributes to guests,
this sets you up for mistakes. Instead, I would envision you
scanning the whole CPUID range "reserved" for virtualization
(starting at 0x40000000) and see whether you get back
anything other than the Hyper-V identification (much like the
way xen_cpuid_base() scans for the Xen range). Of course
that's under the premise that you're right in assuming Hyper-V
would never emulate any other hypervisor's interface.

Jan

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