lkml.org 
[lkml]   [2008]   [Mar]   [27]   [last100]   RSS-feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
Complete thread (EXPERIMENTAL)
/
DateFri, 28 Mar 2008 00:50:39 +0100
FromBjörn Steinbrink <>
SubjectRe: 2.6.25-rc6: BUG: unable to handle kernel NULL pointer dereference
Digg This
On 2008.03.27 16:20:53 +0100, Thomas Gleixner wrote:
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 <mingo@elte.hu>
Date: Thu Mar 27 15:58:28 CET 2008

some early Athlon XP's and Opterons generate bogus faults on prefetch
^^

Umh, XP? Didn't you say X2 above? And looking at the patch, X2 seems more plausible as well, I don't think that the XP supported the NX bit, did it?

Björn

instructions. The workaround for this regressed over .24 - reinstate it.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
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/


\
ISP Services
Valid XHTML 1.0!\ /
Valid CSS! Last update: 2008-03-28 00:53    [W:0.469 / U:1.120 seconds]
©2003-2005 Jasper Spaans