lkml.org 
[lkml]   [2008]   [Mar]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: 2.6.25-rc6: BUG: unable to handle kernel NULL pointer dereference
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/

\
 
 \ /
  Last update: 2008-03-28 00:53    [W:0.093 / U:0.392 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site