mm: numa: do not clear PTE for pte_numa update

mm: numa: do not clear PTE for pte_numa update

The TLB must be flushed if the PTE is updated but change_pte_range is
clearing the PTE while marking PTEs pte_numa without necessarily flushing
the TLB if it reinserts the same entry.  Without the flush, it's
conceivable that two processors have different TLBs for the same virtual
address and at the very least it would generate spurious faults.  This
patch only unmaps the pages in change_pte_range for a full protection
change.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Alex Thorlton <athorlton@sgi.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>