This fixes a potentially bad (although very rarely triggered) bug in the
ppc64 hugepage code.

hpte_update() did not correctly calculate the address for hugepages, so
pte_clear() (which we use for hugepage ptes as well as normal ones)
would not correctly flush the hash page table entry.  Under the right
circumstances this could potentially lead to duplicate hash entries,
which is very bad.

davem's upcoming patch to pass the virtual address directly to set_pte()
and its ilk will obsolete this, but this is bad enough it should
probably be fixed in the meantime.
Signed-off-by: David Gibson <dwg@au1.ibm.com>
Acked-by: William Irwin <wli@holomorphy.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>