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Subject: Re: [PATCH 1/2] VMware detection support for x86 and x86-64
From: Zachary Amsden <zach@vmware.com>
To: "Valdis.Kletnieks@vt.edu" <Valdis.Kletnieks@vt.edu>
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Date: Fri, 26 Sep 2008 13:35:48 -0700
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On Fri, 2008-09-26 at 06:22 -0700, Valdis.Kletnieks@vt.edu wrote:
> On Fri, 26 Sep 2008 14:47:21 +0200, Gerd Hoffmann said:
> >   Hi,
> > 
> > > This, of course, is what CPUID is for.
> > 
> > ... except that it doesn't always work.  It requires vmx/svm, otherwise
> > cpuid doesn't trap and thus can't be filled by the hypervisor ...
> 
> Which would be hardware implementers in the '80s getting wrong the first few
> times what IBM did right the first time.  Doesn't *anybody* do literature
> searches before doing stuff anymore? ;)

>>From your description, IBM also did it wrong the first time.  Having an
instruction which operates differently when running on bare metal vs. in
a hypervisor is never acceptible unless the instruction is trappable.

There will always be a guest which refuses to operate propely in a
hypervisor, either by defect or by design, so 'sensitive' instructions
should always be trappable.  Do it right and you can nest recursively ;)

Zach