PAE removal patch for testing

[Luoqi Chen]

> > 
> >    I've reviewed it as well and it definitely is a bug that 
> needs to be fixed
> > ASAP. Basically, the pmap_remove code in -stable doesn't handle 
> the case of
> > crossing a page table boundry properly. If the next page table 
> page isn't
> > currently mapped, then the kernel will [fatally] fault when 
> trying to access
> > it.
> 
>    Hmmm...after pushing send I'm wondering if I'm mistaken about 
> the problem.
> Nevermind. :-)
> 
> -DG
> 
The real problem is pmap_remove_pte() code could block (when releasing
a pte page), allowing another process to come in and change the temporary
pde mapping (PMAP1). The old pmap code used APTD for this mapping, so
theoretically had the same problem, but APTD was much less frequently
used...

-lq