linux-kernel - Re: [PATCH 1/2] VMware detection support for x86 and x86-64

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Message-Id: <1222461348.27056.201.camel@bodhitayantram.eng.vmware.com>
Date:	Fri, 26 Sep 2008 13:35:48 -0700
From:	Zachary Amsden <zach@...are.com>
To:	"Valdis.Kletnieks@...edu" <Valdis.Kletnieks@...edu>
Cc:	Gerd Hoffmann <kraxel@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Alok Kataria <akataria@...are.com>,
	Alok kataria <alokkataria1@...il.com>,
	Ingo Molnar <mingo@...e.hu>, Yan Li <elliot.li.tech@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"joerg.roedel@....com" <joerg.roedel@....com>,
	"rjmaomao@...il.com" <rjmaomao@...il.com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Hecht <dhecht@...are.com>
Subject: Re: [PATCH 1/2] VMware detection support for x86 and x86-64

On Fri, 2008-09-26 at 06:22 -0700, Valdis.Kletnieks@...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

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