From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758776AbYGaWN6 (ORCPT ); Thu, 31 Jul 2008 18:13:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759989AbYGaWNI (ORCPT ); Thu, 31 Jul 2008 18:13:08 -0400 Received: from 1wt.eu ([62.212.114.60]:2321 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759937AbYGaWNH (ORCPT ); Thu, 31 Jul 2008 18:13:07 -0400 Date: Fri, 1 Aug 2008 00:11:45 +0200 From: Willy Tarreau To: Andrew Morton Cc: Krzysztof Helt , hpa@zytor.com, linux-kernel@vger.kernel.org, Ingo Molnar , Jeremy Fitzhardinge Subject: Re: [PATCH] x86: fdiv bug detection fix Message-ID: <20080731221145.GD615@1wt.eu> References: <20080731234344.eb3c4ed2.krzysztof.h1@wp.pl> <20080731144920.0016e02d.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080731144920.0016e02d.akpm@linux-foundation.org> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 31, 2008 at 02:49:20PM -0700, Andrew Morton wrote: > On Thu, 31 Jul 2008 23:43:44 +0200 > Krzysztof Helt wrote: > > > From: Krzysztof Helt > > > > The fdiv detection code writes s32 integer into > > the boot_cpu_data.fdiv_bug. > > However, the boot_cpu_data.fdiv_bug is only char (s8) > > field so the detection overwrites already set fields for > > other bugs, e.g. the f00f bug field. > > > > Use local s32 variable to receive result. > > > > Signed-off-by: Krzysztof Helt > > --- > > > > This is a partial fix to Bugzilla #9928 - fixes wrong > > information about the f00f bug (tested) and probably > > for coma bug (I have no cpu to test this). > > > > diff -urp linux-alsa/arch/x86/kernel/cpu/bugs.c linux-new/arch/x86/kernel/cpu/bugs.c > > --- linux-alsa/arch/x86/kernel/cpu/bugs.c 2008-07-31 12:40:31.000000000 +0200 > > +++ linux-new/arch/x86/kernel/cpu/bugs.c 2008-07-31 23:24:07.722657435 +0200 > > @@ -50,6 +50,8 @@ static double __initdata y = 3145727.0; > > */ > > static void __init check_fpu(void) > > { > > + s32 fdiv_bug; > > + > > if (!boot_cpu_data.hard_math) { > > #ifndef CONFIG_MATH_EMULATION > > printk(KERN_EMERG "No coprocessor found and no math emulation present.\n"); > > @@ -74,8 +76,10 @@ static void __init check_fpu(void) > > "fistpl %0\n\t" > > "fwait\n\t" > > "fninit" > > - : "=m" (*&boot_cpu_data.fdiv_bug) > > + : "=m" (*&fdiv_bug) > > : "m" (*&x), "m" (*&y)); > > + > > + boot_cpu_data.fdiv_bug = fdiv_bug; > > if (boot_cpu_data.fdiv_bug) > > printk("Hmm, FPU with FDIV bug.\n"); > > } > > hm, the code seems to have been that way for quite some time. Indeed! since boot_cpu_data.fdiv_bug was declared as an int in 2.4, I think it might have changed when a lot of code was moved from asm/*.h to arch/*.c. > I wonder why nobody noticed this before. For the same reason those bugs were noticed very late in the products' lifetime I guess : because unless someone actively plays with them on your machine, you hardly trigger them by accident. Willy