Keir Fraser wrote:
>
> We cannot use pte_clear() unless we redefine it for PAE. Currently it 
> reduces to set_pte() which explicitly uses the wrong ordering (sets 
> high *then* low, because it's normally used to introduce a mapping).

Yes, that means pte_clear() has the same bug.  Why don't we redefine 
pte_clear for PAE?  Then the ifdef can go away.

> Also, I think wmb() should be used in PAE's set_pte(), rather than the 
> current smp_wmb(). They reduce to the same thing, but wmb() makes it 
> clear this is is not an issue specific to SMP systems. 

I agree with that.  The problem is not related to SMP at all.  I would 
propose this approach.