[PATCH 2.6.14] mm: 8xx MM fix for

[Joakim Tjernlund]

> Joakim!
> 
> On Mon, Nov 07, 2005 at 03:32:52PM +0100, Joakim Tjernlund wrote:
> > Hi Marcelo
> > 
> > [SNIP] 
> > > The root of the problem are the changes against the 8xx TLB 
> > > handlers introduced
> > > during v2.6. What happens is the TLBMiss handlers load the 
> > > zeroed pte into
> > > the TLB, causing the TLBError handler to be invoked (thats 
> > > two TLB faults per 
> > > pagefault), which then jumps to the generic MM code to 
> setup the pte.
> > > 
> > > The bug is that the zeroed TLB is not invalidated (the same reason
> > > for the "dcbst" misbehaviour), resulting in infinite 
> TLBError faults.
> > > 
> > > Dan, I wonder why we just don't go back to v2.4 behaviour.
> > 
> > This is one reason why it is the way it is:
> > 
> http://ozlabs.org/pipermail/linuxppc-embedded/2005-January/016382.html
> > This details are little fuzzy ATM, but I think the reason for the
> > current
> > impl. was only that it was less intrusive to impl.
> 
> Ah, I see. I wonder if the bug is processor specific: we 
> don't have such
> changes in our v2.4 tree and never experienced such problem.
> 
> It should be pretty easy to hit it right? (instruction 
> pagefaults should
> fail).

No, its pretty hard to trigger it. Read the all mails on the subject to
see why.
The one or two exception approach doesn't matter performancewise(at
least for ITLB exceptions)
I think.

> 
> Grigori, Tom, can you enlight us about the issue on the URL above. How
> can it be triggered?
> 
> 
> 
>