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From: KY Srinivasan <kys@microsoft.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: "olaf@aepfle.de" <olaf@aepfle.de>, "bp@alien8.de" <bp@alien8.de>,
	"apw@canonical.com" <apw@canonical.com>,
	"x86@kernel.org" <x86@kernel.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"jasowang@redhat.com" <jasowang@redhat.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"hpa@zytor.com" <hpa@zytor.com>
Subject: RE: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V
Date: Wed, 30 Jan 2013 18:12:17 +0000	[thread overview]
Message-ID: <1db4d98aa3434d4eab7b36bbeb89cd47@SN2PR03MB061.namprd03.prod.outlook.com> (raw)
In-Reply-To: <5108ED9702000078000BAA08@nat28.tlf.novell.com>



> -----Original Message-----
> From: Jan Beulich [mailto:JBeulich@suse.com]
> Sent: Wednesday, January 30, 2013 3:53 AM
> To: KY Srinivasan
> Cc: olaf@aepfle.de; bp@alien8.de; apw@canonical.com; x86@kernel.org;
> tglx@linutronix.de; devel@linuxdriverproject.org; gregkh@linuxfoundation.org;
> jasowang@redhat.com; linux-kernel@vger.kernel.org; hpa@zytor.com
> Subject: Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V
> 
> >>> On 30.01.13 at 01:51, "K. Y. Srinivasan" <kys@microsoft.com> wrote:
> > Xen emulates Hyper-V to host enlightened Windows. Looks like this
> > emulation may be turned on by default even for Linux guests. Check and
> > fail Hyper-V detection if we are on Xen.
> >
> > Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> > ---
> >  arch/x86/kernel/cpu/mshyperv.c |    7 +++++++
> >  1 files changed, 7 insertions(+), 0 deletions(-)
> >
> > diff --git a/arch/x86/kernel/cpu/mshyperv.c
> b/arch/x86/kernel/cpu/mshyperv.c
> > index 646d192..4dab317 100644
> > --- a/arch/x86/kernel/cpu/mshyperv.c
> > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > @@ -30,6 +30,13 @@ static bool __init ms_hyperv_platform(void)
> >  	if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))
> >  		return false;
> >
> > +	/*
> > +	 * Xen emulates Hyper-V to support enlightened Windows.
> > +	 * Check to see first if we are on a Xen Hypervisor.
> > +	 */
> > +	if (xen_cpuid_base())
> > +		return false;
> > +
> >  	cpuid(HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS,
> >  	      &eax, &hyp_signature[0], &hyp_signature[1], &hyp_signature[2]);
> 
> I'm not convinced that's the right approach - any hypervisor
> could do similar emulation, and hence you either want to make
> sure you run on Hyper-V (by excluding all others), or you
> tolerate using the emulation (which may require syncing up with
> the other guest implementations so that shared resources don't
> get used by two parties).
> 
> I also wonder whether using the Hyper-V emulation (where
> useful, there might not be anything right now, but this may
> change going forward) when no Xen support is configured
> wouldn't be better than not using anything...

Jan,

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. 

Regards,

K. Y



  reply	other threads:[~2013-01-30 18:16 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-01-30  0:51 [PATCH 0/3] X86: Deliver Hyper-V interrupts on a seperate IDT vector K. Y. Srinivasan
2013-01-30  0:51 ` [PATCH 1/3] x86: Hyper-V: register clocksource only if its advertised K. Y. Srinivasan
2013-01-30  0:51   ` [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V K. Y. Srinivasan
2013-01-30  8:53     ` Jan Beulich
2013-01-30 18:12       ` KY Srinivasan [this message]
2013-01-30 18:19         ` H. Peter Anvin
2013-01-31  7:37         ` Jan Beulich
2013-01-31 14:46           ` KY Srinivasan
2013-01-31 15:53             ` KY Srinivasan
2013-01-31 16:45               ` Jan Beulich
2013-01-31 18:29                 ` H. Peter Anvin
2013-01-31 21:41       ` H. Peter Anvin
2013-02-01 13:19         ` Stefano Stabellini
2013-02-01 15:10           ` KY Srinivasan
2013-02-01 19:34             ` KY Srinivasan
2013-01-30  0:51   ` [PATCH 3/3] X86: Handle Hyper-V vmbus interrupts as special hypervisor interrupts K. Y. Srinivasan
2013-01-30  8:58     ` Jan Beulich
2013-01-31 14:55       ` KY Srinivasan
2013-02-04  1:21 [PATCH 0/3] X86: Deliver Hyper-V interrupts on a seperate IDT vector K. Y. Srinivasan
2013-02-04  1:22 ` [PATCH 1/3] x86: Hyper-V: register clocksource only if its advertised K. Y. Srinivasan
2013-02-04  1:22   ` [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V K. Y. Srinivasan
2013-04-17  7:06     ` Michael S. Tsirkin
2013-04-17 13:20       ` KY Srinivasan
2013-04-17 12:48         ` Michael S. Tsirkin
2013-04-17 14:12           ` KY Srinivasan
2013-04-17 13:25             ` Michael S. Tsirkin
2013-04-17 14:34               ` KY Srinivasan
2013-04-17 13:48                 ` Michael S. Tsirkin
2013-04-17 15:31                   ` KY Srinivasan
2013-04-17 15:50                     ` Jan Beulich
2013-04-17 16:28                       ` KY Srinivasan
2013-04-18  7:48                         ` Michael S. Tsirkin
2013-04-18 13:23                           ` KY Srinivasan
2013-04-18 13:30                             ` KY Srinivasan
2013-04-17 13:52         ` Jan Beulich
2013-04-17 13:01           ` Michael S. Tsirkin
2013-04-17 13:11             ` Michael S. Tsirkin
2013-04-17 14:09             ` Jan Beulich
2013-04-17 15:17               ` H. Peter Anvin

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