linux-kernel - Re: [BUG] x86 kenel won't boot under Virtual PC

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Message-ID: <20080831122751.72afafb5@infradead.org>
Date:	Sun, 31 Aug 2008 12:27:51 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Sanders <linux@...dersweb.net>, linux-kernel@...r.kernel.org,
	Jan Beulich <jbeulich@...ell.com>, Andi Kleen <ak@...e.de>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [BUG] x86 kenel won't boot under Virtual PC

On Sun, 31 Aug 2008 11:47:04 -0700 (PDT)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 
> 
> On Sun, 31 Aug 2008, David Sanders wrote:
> >
> > I recently discovered that x86 kernels won't boot under Virtual PC.
> 
> What CPU does Virtual PC emulate? As far as Wikipedia is concerned
> (not that I'd take it on complete faith) it emulates a 32-bit Intel
> Pentium II.
> 
> And that commit makes the kernel use the "P6 nops" for such hardware. 
> Maybe Virtual PC doesn't support the newer intel nop things?
> 
> Intel docs say that it should be available on any intel CPU that has 
> CPUID.01H.EAX[11:8] = 0110B or 1111B. That's the "family ID", and
> Pentium II should have a family ID of 6 (ie that 0110B case).
> 
> So it sounds like a Virtual PC bug, but I dunno. And maybe we should
> just use the legcay nops for anything that isn't modern (ie P4+ or
> Core)?

it's probably even a security bug in that I don't see what would be
stopping a ring 3 user process from executing these instructions...

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