linux-kernel - Re: nops in virtual pc x86

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Message-ID: <48CAEB40.9090303@zytor.com>
Date:	Fri, 12 Sep 2008 15:20:48 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	David Sanders <linux@...dersweb.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: nops in virtual pc x86

Linus Torvalds wrote:
> 
> The thing is, afaik, Virtual PC will happily let the CPU execute all the 
> user-space instructions, and thus they all work as well as if they were 
> running on real hardware - since they _do_ run on real hardware.
> 
> But it is probably the case that Virtual PC will then do some "security 
> checking" of any system code, possibly by JIT'ing it or just interpreting 
> it, since it can't let the kernel run natively with privileges. That's 
> what VMware does too, since older CPU's don't have virtualization support 
> for ring0 programs.
> 
> And _that_ is presumably buggy, and never learnt about the "new" 
> instructions in the PPro.
> 

Actually, it's apparently worse than that.  The NOPL probe instruction 
for dynamic testing gets executed in kernel space, and passes! 
Apparently at that point (and beyond) it is okay, though.

Microsoft quality stuff.

	-hpa
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