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

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Message-ID: <510AE4F6.1050407@zytor.com>
Date:	Thu, 31 Jan 2013 13:41:10 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jan Beulich <JBeulich@...e.com>
CC:	"K. Y. Srinivasan" <kys@...rosoft.com>, 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
Subject: Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V

On 01/30/2013 12:53 AM, Jan Beulich wrote:
> 
> 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...
> 

I'm confused about "the right approach" here is.  As far as I
understand, this only can affect a Xen guest where HyperV guest support
is enabled but not Xen support, and only because Xen emulates HyperV but
does so incorrectly.

This is a Xen bug, and as such it makes sense to reject Xen
specifically.  If another hypervisor emulates HyperV and does so
correctly there seems to be no reason to reject it.

	-hpa


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