linux-kernel - Re: [PATCH] kmemcheck: disable fast string operations on P4 CPUs

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Message-ID: <49A0C2D4.20009@zytor.com>
Date:	Sat, 21 Feb 2009 19:13:24 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vegard Nossum <vegard.nossum@...il.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ingo Molnar <mingo@...e.hu>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH] kmemcheck: disable fast string operations on P4 CPUs

Vegard Nossum wrote:
> This patch may allow us to remove the REP emulation code from
> kmemcheck.

> +#ifdef CONFIG_KMEMCHECK
> +	/*
> +	 * P4s have a "fast strings" feature which causes single-
> +	 * stepping REP instructions to only generate a #DB on
> +	 * cache-line boundaries.
> +	 *
> +	 * Ingo Molnar reported a Pentium D (model 6) and a Xeon
> +	 * (model 2) with the same problem.
> +	 */
> +	if (c->x86 == 15) {

If this is supposed to refer to the Intel P4 core, you should exclude
the post-P4 cores that also have x86 == 15 (e.g. Core 2 and Core i7).
If those are affected, too, they should be mentioned in the comment.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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