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Date: Sun, 22 Feb 2009 11:51:33 +0100 From: Vegard Nossum <vegard.nossum@...il.com> To: "H. Peter Anvin" <hpa@...or.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 2009/2/22 H. Peter Anvin <hpa@...or.com>: > 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. Thanks for the review! This is supposed to happen only for those machines where the "fast string ops" is enabled by default. We have a test for that in the part that you snipped -- and since the MSR is architectural, I believe it would exist (i.e. not cause an error if we read it, but just be cleared by default or hard-wired to clear) on those post-P4 cores you mentioned too? Vegard -- "The animistic metaphor of the bug that maliciously sneaked in while the programmer was not looking is intellectually dishonest as it disguises that the error is the programmer's own creation." -- E. W. Dijkstra, EWD1036 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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