Commit 8b1f3124 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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[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 <>

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: default avatarNick Piggin <>
Signed-off-by: default avatarHugh Dickins <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 95001ee9
......@@ -158,6 +158,19 @@ static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addres
#define lazy_mmu_prot_update(pte) do { } while (0)
#define move_pte(pte, prot, old_addr, new_addr) (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; \
* When walking page tables, get the address of the next boundary,
* or the end address of the range if that comes earlier. Although no
......@@ -68,6 +68,8 @@ extern unsigned long zero_page_mask;
#define ZERO_PAGE(vaddr) \
(virt_to_page(empty_zero_page + (((unsigned long)(vaddr)) & zero_page_mask)))
extern void paging_init(void);
......@@ -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;
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