[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>
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index f86c1e5..ff28c8b 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -158,6 +158,19 @@
#define lazy_mmu_prot_update(pte) do { } while (0)
#endif
+#ifndef __HAVE_ARCH_MULTIPLE_ZERO_PAGE
+#define move_pte(pte, prot, old_addr, new_addr) (pte)
+#else
+#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; \
+})
+#endif
+
/*
* When walking page tables, get the address of the next boundary,
* or the end address of the range if that comes earlier. Although no
diff --git a/include/asm-mips/pgtable.h b/include/asm-mips/pgtable.h
index cbd1672..eaf5d9b 100644
--- a/include/asm-mips/pgtable.h
+++ b/include/asm-mips/pgtable.h
@@ -68,6 +68,8 @@
#define ZERO_PAGE(vaddr) \
(virt_to_page(empty_zero_page + (((unsigned long)(vaddr)) & zero_page_mask)))
+#define __HAVE_ARCH_MULTIPLE_ZERO_PAGE
+
extern void paging_init(void);
/*
diff --git a/mm/mremap.c b/mm/mremap.c
index a32fed4..f343fc7 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -141,10 +141,10 @@
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;