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

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Message-ID: <4E2F0068.1080001@redhat.com>
Date:	Tue, 26 Jul 2011 20:59:04 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Borislav Petkov <bp@...64.org>
CC:	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <borislav.petkov@....com>,
	Andre Przywara <andre.przywara@....com>,
	Martin Pohlack <martin.pohlack@....com>
Subject: Re: [PATCH] x86, AMD: Correct F15h IC aliasing issue

On 07/22/2011 04:15 PM, Borislav Petkov wrote:
> From: Borislav Petkov<borislav.petkov@....com>
>
> This patch provides performance tuning for the "Bulldozer" CPU. With its
> shared instruction cache there is a chance of generating an excessive
> number of cache cross-invalidates when running specific workloads on the
> cores of a compute module.
>
> This excessive amount of cross-invalidations can be observed if cache
> lines backed by shared physical memory alias in bits [14:12] of their
> virtual addresses, as those bits are used for the index generation.
>
> This patch addresses the issue by zeroing out the slice [14:12] of
> the file mapping's virtual address at generation time, thus forcing
> those bits the same for all mappings of a single shared library across
> processes and, in doing so, avoids instruction cache aliases.
>
> It also adds the kernel command line option
> "unalias_va_addr=(32|64|off)" with which virtual address unaliasing
> can be enabled for 32-bit or 64-bit x86 individually, or be completely
> disabled.
>
> This change leaves virtual region address allocation on other families
> and/or vendors unaffected.
>

Is it possible to derive the bit positions (and the need to mask them) 
from the cpuid description of the cache topology and sizes?

-- 
error compiling committee.c: too many arguments to function

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