Hi Andrea,

Are you sure that BUG_ON() should be for !page_count(kpte_page)?  I
noticed that I was getting some BUGs when the count went back to 0, but
the pte page was completely full with valid ptes.  I *think* it's
correct to make it:

       BUG_ON(page_count(kpte_page) < 0);

Or, I guess we could keep the old BUG_ON(), and put it inside the else
block with the __put_page().  

-- Dave