[PATCH] mm: mremap correct rmap accounting

Nick Piggin points out that page accounting on MIPS multiple ZERO_PAGEs
is not maintained by its move_pte, and could lead to freeing a ZERO_PAGE.

Instead of complicating that move_pte, just forget the minor optimization
when mremapping, and change the one thing which needed it for correctness
- filemap_xip use ZERO_PAGE(0) throughout instead of according to address.

[ "There is no block device driver one could use for XIP on mips
   platforms" - Carsten Otte ]

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Carsten Otte <cotte@de.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-mips/pgtable.h

@@ -69,16 +69,6 @@ extern unsigned long zero_page_mask;
 #define ZERO_PAGE(vaddr) \
 	(virt_to_page((void *)(empty_zero_page + (((unsigned long)(vaddr)) & zero_page_mask))))
 
-#define __HAVE_ARCH_MOVE_PTE
-#define move_pte(pte, prot, old_addr, new_addr)				\
-({									\
- 	pte_t newpte = (pte);						\
-	if (pte_present(pte) && pfn_valid(pte_pfn(pte)) &&		\
-			pte_page(pte) == ZERO_PAGE(old_addr))		\
-		newpte = mk_pte(ZERO_PAGE(new_addr), (prot));		\
-	newpte;								\
-})
-
 extern void paging_init(void);
 
 /*