Re: 2.6.25-rc6: BUG: unable to handle kernel NULL pointerdereference

[Ingo Molnar]

* Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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.

can also be tested by picking up x86.git/latest, which has this patch 
included:

   http://people.redhat.com/mingo/x86.git/README

	Ingo
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