[PPC64] Hugepage hash flushing bugfix

[David Gibson]

Andrew, Linus, please apply:

Fix 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 at au1.ibm.com>

Index: working-2.6/arch/ppc64/mm/tlb.c
===================================================================
--- working-2.6.orig/arch/ppc64/mm/tlb.c	2004-09-09 09:59:49.000000000 +1000
+++ working-2.6/arch/ppc64/mm/tlb.c	2005-02-25 14:56:47.000000000 +1100
@@ -85,8 +85,12 @@
 
 	ptepage = virt_to_page(ptep);
 	mm = (struct mm_struct *) ptepage->mapping;
-	addr = ptepage->index +
-		(((unsigned long)ptep & ~PAGE_MASK) * PTRS_PER_PTE);
+	addr = ptepage->index;
+	if (pte_huge(pte))
+		addr +=  ((unsigned long)ptep & ~PAGE_MASK)
+			/ sizeof(*ptep) * HPAGE_SIZE;
+	else
+		addr += ((unsigned long)ptep & ~PAGE_MASK) * PTRS_PER_PTE;
 
 	if (REGION_ID(addr) == USER_REGION_ID)
 		context = mm->context.id;


-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist.  NOT _the_ _other_ _way_
				| _around_!
http://www.ozlabs.org/people/dgibson