linux-kernel - Re: [PATCH] x86, AMD: Correct F15h IC aliasing issue

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Message-ID: <20110726172801.GC32536@aftab>
Date:	Tue, 26 Jul 2011 19:28:01 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Ray Lee <ray-lk@...rabbit.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"Przywara, Andre" <Andre.Przywara@....com>,
	"Pohlack, Martin" <Martin.Pohlack@....com>
Subject: Re: [PATCH] x86, AMD: Correct F15h IC aliasing issue

On Tue, Jul 26, 2011 at 01:58:43AM -0400, Ray Lee wrote:
> > > Are only 1% of mappings 'bad'? 5%? 10%? 50%? We have no idea and the
> > > actual number matters a lot.
> >
> > Actually, it's hard to say what is a 'good' and 'bad' allocation. If
> > they don't alias, they're always good :).
> 
> Count the number of aliases per total mappings, and report that as a
> failure percentage? It doesn't have to be a perfect metric, it just
> needs to be a meaningful and repeatable one.

Ok, I went and installed a Debian wheezy with gnome and started almost
everything I could find in the startup menu. Kernel is 3.0 with Linus'
simpler fix.

The attached file shows all libraries which would create aliases (i.e. 2
or more unique values for bits [14:12] along with the respective count)
in the total of:

Total r-xp mappings: 831, aliasing: 240 (0.289%)

For example, libc gets mapped into all possible slots for [14:12]

Library                                 [14:12] count
=======                                 ======= =====
/lib/libc-2.11.2.so
                                        0       12
                                        1       12
                                        2       11
                                        3       12
                                        4       13
                                        5       16
                                        6       13
                                        7       9


and so on.

So we're close to 30% and could get higher with more apps. I guess I'll
start working on the review comments to the more involved fix.

Thanks.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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View attachment "simple-fix-results.txt" of type "text/plain" (18293 bytes)