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

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Message-ID: <32e50a43db8849f2944db256989bebb8@SN2PR03MB061.namprd03.prod.outlook.com>
Date:	Thu, 31 Jan 2013 14:46:24 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Jan Beulich <JBeulich@...e.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



> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@...e.com]
> Sent: Thursday, January 31, 2013 2:38 AM
> To: KY Srinivasan
> Cc: olaf@...fle.de; bp@...en8.de; apw@...onical.com; x86@...nel.org;
> tglx@...utronix.de; devel@...uxdriverproject.org; gregkh@...uxfoundation.org;
> jasowang@...hat.com; linux-kernel@...r.kernel.org; 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.

Agreed; I will make the appropriate changes as you have recommended.

Regards,

K. Y


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