Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758420AbYC0PWZ (ORCPT ); Thu, 27 Mar 2008 11:22:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755382AbYC0PWS (ORCPT ); Thu, 27 Mar 2008 11:22:18 -0400 Received: from www.tglx.de ([62.245.132.106]:35036 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754534AbYC0PWR (ORCPT ); Thu, 27 Mar 2008 11:22:17 -0400 Date: Thu, 27 Mar 2008 16:20:53 +0100 (CET) From: Thomas Gleixner To: Andrew Morton cc: Christian Kujau , LKML , Markus Rehbach , "Rafael J. Wysocki" , Ingo Molnar Subject: Re: 2.6.25-rc6: BUG: unable to handle kernel NULL pointer dereference In-Reply-To: <20080325233357.17d6ac41.akpm@linux-foundation.org> Message-ID: References: <20080325233357.17d6ac41.akpm@linux-foundation.org> User-Agent: Alpine 1.00 (LFD 882 2007-12-20) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1954 Lines: 61 On Tue, 25 Mar 2008, Andrew Morton wrote: > > Code: 53 c0 e8 20 08 fc ff c1 e3 02 8b 14 33 89 54 24 20 8b 44 24 20 85 c0 75 10 eb 51 8b 12 89 54 24 20 8b 44 24 20 85 c0 74 43 8b 02 <0f> 18 00 90 8d 5a d8 39 6b 34 75 e4 8b 7c 24 0c 39 7b 30 75 db It faults in a prefetch. > Markus reported what looks to be the same thing here: > http://lkml.org/lkml/2008/3/21/202 and it's already in the regresison list. Same here. And both are AMD X2 early stepping machines. > I guess you've confirmed that this wasn't a mystery > once-off-on-that-machine. > > I can't think what we did to cause this. I had a lengthy bug decoding session with Ingo and we found the root cause: A dropped workaround for the prefetch bug in early X2s and Opterons. Patch below. Thanks, tglx ---------------> Subject: x86: fix prefetch workaround From: Ingo Molnar Date: Thu Mar 27 15:58:28 CET 2008 some early Athlon XP's and Opterons generate bogus faults on prefetch instructions. The workaround for this regressed over .24 - reinstate it. Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner --- arch/x86/mm/fault.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) Index: linux-x86.q/arch/x86/mm/fault.c =================================================================== --- linux-x86.q.orig/arch/x86/mm/fault.c +++ linux-x86.q/arch/x86/mm/fault.c @@ -104,7 +104,8 @@ static int is_prefetch(struct pt_regs *r unsigned char *max_instr; #ifdef CONFIG_X86_32 - if (!(__supported_pte_mask & _PAGE_NX)) + /* Catch an obscure case of prefetch inside an NX page: */ + if ((__supported_pte_mask & _PAGE_NX) && (error_code & 16)) return 0; #endif -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/