linux-kernel - Re: [patch 1/2] F00F bug fixup for i386

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Date:	Sat, 14 Jul 2007 11:22:39 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] F00F bug fixup for i386 - use immediate values

On Fri, Jul 13, 2007 at 09:26:43PM -0400, Mathieu Desnoyers wrote:
> Use the faster immediate values for F00F bug handling in do_page_fault.

> --- linux-2.6-lttng.orig/arch/i386/mm/fault.c
> +++ linux-2.6-lttng/arch/i386/mm/fault.c
> @@ -492,7 +493,7 @@
>  	/*
>  	 * Pentium F0 0F C7 C8 bug workaround.
>  	 */
> -	if (boot_cpu_data.f00f_bug) {
> +	immediate_if (&f00f_bug_fix) {

This code is not called during normal pagefaults and even during invalid
userspace accesses.

Out of curiosity, I inserted printk() at this place to see where I was
wrong. I got only two hits:

	Checking if this processor honours the WP bit even in supervisor mode... do_page_fault:
	Freeing unused kernel memory: 116k freed
	do_page_fault:

Resume: nobody gives a fuck about performance of this particular if,
	so conversion it totally pointless.

-
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