From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [RFC PATCH] Emulate MOVBE
Date: Wed, 10 Apr 2013 13:21:37 +0300
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Cc: Andre Przywara <andre@andrep.de>, kvm@vger.kernel.org,
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	"H. Peter Anvin" <hpa@zytor.com>, x86-ml <x86@kernel.org>,
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To: Borislav Petkov <bp@alien8.de>
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On Wed, Apr 10, 2013 at 12:17:21PM +0200, Borislav Petkov wrote:
> On Wed, Apr 10, 2013 at 01:08:46PM +0300, Gleb Natapov wrote:
> > We can add the emulation, but we should not start announcing the
> > instruction availability to a guest if host cpu does not have it
> > by default. This may trick a guest into thinking that movbe is the
> > fastest way to do something when it is not.
> 
> That could be a problem because kernels compiled for atom look at CPUID
> to check for MOVBE support and refuse to continue if there's none.
> 
You will still be able to force it on qemu command line by adding +movbe
to cpu definition, it just not be the default.


--
			Gleb.