Messages in this thread | | | Date | Fri, 28 Mar 2008 00:50:39 +0100 | From | Björn Steinbrink <> | Subject | Re: 2.6.25-rc6: BUG: unable to handle kernel NULL pointer dereference |
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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/
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