Messages in this thread Patch in this message | | | Date | Thu, 27 Mar 2008 16:20:53 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: 2.6.25-rc6: BUG: unable to handle kernel NULL pointer dereference |
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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 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
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