[PATCH] mm: move_pte to remap ZERO_PAGE

Move the ZERO_PAGE remapping complexity to the move_pte macro in
asm-generic, have it conditionally depend on
__HAVE_ARCH_MULTIPLE_ZERO_PAGE, which gets defined for MIPS.

For architectures without __HAVE_ARCH_MULTIPLE_ZERO_PAGE, move_pte becomes
a noop.

From: Hugh Dickins <hugh@veritas.com>

Fix nasty little bug we've missed in Nick's mremap move ZERO_PAGE patch.
The "pte" at that point may be a swap entry or a pte_file entry: we must
check pte_present before perhaps corrupting such an entry.

Patch below against 2.6.14-rc2-mm1, but the same bug is in 2.6.14-rc2's
mm/mremap.c, and more dangerous there since it's affecting all arches: I
think the safest course is to send Nick's patch and Yoichi's build fix and
this fix (build tested) on to Linus - so only MIPS can be affected.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/mm/mremap.c b/mm/mremap.c
index a32fed454bd7..f343fc73a8bd 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -141,10 +141,10 @@ move_one_page(struct vm_area_struct *vma, unsigned long old_addr,
                         if (dst) {
                                 pte_t pte;
                                 pte = ptep_clear_flush(vma, old_addr, src);
+
                                 /* ZERO_PAGE can be dependant on virtual addr */
-                                if (pfn_valid(pte_pfn(pte)) &&
-                                        pte_page(pte) == ZERO_PAGE(old_addr))
-                                        pte = pte_wrprotect(mk_pte(ZERO_PAGE(new_addr), new_vma->vm_page_prot));
+                                pte = move_pte(pte, new_vma->vm_page_prot,
+                                                        old_addr, new_addr);
                                 set_pte_at(mm, new_addr, dst, pte);
                         } else
                                 error = -ENOMEM;