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

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Message-ID: <20110725215328.GA25960@aftab>
Date:	Mon, 25 Jul 2011 23:53:28 +0200
From:	Borislav Petkov <bp@...64.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Borislav Petkov <bp@...64.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 Mon, Jul 25, 2011 at 04:06:45PM -0400, Ingo Molnar wrote:
> 
> * Borislav Petkov <bp@...64.org> wrote:
> 
> > So yeah, the simpler fix works for processes mapping libraries in 
> > the same order but not for processes mapping a subset of libraries 
> > in a different order.
> 
> but what is the proportion of 'good' versus bad alignment of 
> libraries, could you collect some stats on a representative enough, 
> fully booted up Linux system?
> 
> 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 :).

Anyway, I did some beginners awk-ery on a gentoo system with ca. 150
processes. Below is some data for the "r-xp" mappings.

ld-2.12.2.so, for example, is always loaded at an address with [14:12]
= 000b while libc's addresses differ in those bits because a different
number of allocations is being done between ld and libc, thus libc lands
at different offsets.

I'll do a more comprehensive collection tomorrow and distribute the
mappings by [14:12] value, that should give us a better idea.

/lib64/ld-2.12.2.so|r-xp|7f07f61d8000 1
/lib64/ld-2.12.2.so|r-xp|7f1d8be10000 1
/lib64/ld-2.12.2.so|r-xp|7f1ea7678000 1
/lib64/ld-2.12.2.so|r-xp|7f272e248000 1
/lib64/ld-2.12.2.so|r-xp|7f37acf88000 1
/lib64/ld-2.12.2.so|r-xp|7f49853f0000 1
/lib64/ld-2.12.2.so|r-xp|7f50c1460000 1
/lib64/ld-2.12.2.so|r-xp|7f59f58e0000 1
/lib64/ld-2.12.2.so|r-xp|7f63dc818000 1
/lib64/ld-2.12.2.so|r-xp|7f7267d70000 1
/lib64/ld-2.12.2.so|r-xp|7fa026ba0000 2
/lib64/ld-2.12.2.so|r-xp|7fa24de88000 1
/lib64/ld-2.12.2.so|r-xp|7fa604cf8000 1
/lib64/ld-2.12.2.so|r-xp|7fb07d418000 1
/lib64/ld-2.12.2.so|r-xp|7fc33cb78000 1
/lib64/ld-2.12.2.so|r-xp|7fd0c2770000 1
/lib64/ld-2.12.2.so|r-xp|7fd1e2a08000 1
/lib64/ld-2.12.2.so|r-xp|7fd214b18000 1
/lib64/ld-2.12.2.so|r-xp|7fda88a58000 1
/lib64/ld-2.12.2.so|r-xp|7fdb87d98000 1
/lib64/ld-2.12.2.so|r-xp|7fe42a588000 1
/lib64/ld-2.12.2.so|r-xp|7ffd79c08000 1
/lib64/libc-2.12.2.so|r-xp|7f07f4e3e000 1
/lib64/libc-2.12.2.so|r-xp|7f1d8b66d000 1
/lib64/libc-2.12.2.so|r-xp|7f1ea7315000 1
/lib64/libc-2.12.2.so|r-xp|7f272ceae000 1
/lib64/libc-2.12.2.so|r-xp|7f37acc25000 1
/lib64/libc-2.12.2.so|r-xp|7f498508d000 1
/lib64/libc-2.12.2.so|r-xp|7f50c0ca9000 1
/lib64/libc-2.12.2.so|r-xp|7f59f557d000 1
/lib64/libc-2.12.2.so|r-xp|7f63dc061000 1
/lib64/libc-2.12.2.so|r-xp|7f7267a0d000 1
/lib64/libc-2.12.2.so|r-xp|7fa02591d000 2
/lib64/libc-2.12.2.so|r-xp|7fa24d8a5000 1
/lib64/libc-2.12.2.so|r-xp|7fa604995000 1
/lib64/libc-2.12.2.so|r-xp|7fb07cc31000 1
/lib64/libc-2.12.2.so|r-xp|7fc33b7de000 1
/lib64/libc-2.12.2.so|r-xp|7fd0c1f89000 1
/lib64/libc-2.12.2.so|r-xp|7fd1e26a5000 1
/lib64/libc-2.12.2.so|r-xp|7fd2147b5000 1
/lib64/libc-2.12.2.so|r-xp|7fda884e8000 1
/lib64/libc-2.12.2.so|r-xp|7fdb87a35000 1
/lib64/libc-2.12.2.so|r-xp|7fe42a01c000 1
/lib64/libc-2.12.2.so|r-xp|7ffd79451000 1

Thanks.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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