linux-kernel - Re: i686 quirk for AMD Geode

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Date:	Tue, 10 Nov 2009 23:21:40 +0100
From:	Willy Tarreau <w@....eu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Pavel Machek <pavel@....cz>, Avi Kivity <avi@...hat.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Matteo Croce <technoboy85@...il.com>,
	Sven-Haegar Koch <haegar@...net.de>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: i686 quirk for AMD Geode

On Tue, Nov 10, 2009 at 02:15:55PM -0800, H. Peter Anvin wrote:
> I immediately note that you have absolutely no check on the code
> segment, either in terms of code segment limits or even that we're in
> the right mode.  Furthermore, you read user space -- code in user space
> is still user space -- without get_user().

Yes I remember about that one now. HCH told me about it.

> We also need NX protection
> to be honoured, and the various special subtleties of the x86
> instruction format (15-byte limit, for example) to be preserved: they
> aren't just there randomly, but are there to protect against specific
> failures.

OK.

> *THIS* is the kind of complexity that makes me think that having a
> single source for all interpretation done in the kernel is the preferred
> option.

I understand, your point. We just need to check when it becomes overkill
to use a full-blown emulator of 3 instructions and a few "simple" rules.

Willy

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