path: root/mm
diff options
authorNick Piggin <>2005-09-03 15:54:49 -0700
committerLinus Torvalds <>2005-09-05 00:05:44 -0700
commit9a61c349b28ec5aef7e929236571fd770fdef0bb (patch)
treec78c703dcca91302901d116031b311de7ad3fd78 /mm
parent4d7670e0f649f9e6e6ea6c8bb9f52441fa00f92b (diff)
[PATCH] mm: remap ZERO_PAGE mappings
filemap_xip's nopage routine maps the ZERO_PAGE into readonly mappings, if it has no data page to map there: then if the hole in the file is later filled, __xip_unmap uses an rmap technique to replace the ZERO_PAGEs mapped for that offset by the newly allocated file page, so that established mappings will see the newly written data. However, on MIPS (alone) there's not one but as many as eight ZERO_PAGEs, chosen for coloring by user virtual address; and if mremap has meanwhile been used to move a mapping containing a ZERO_PAGE, it will generally not match the ZERO_PAGE(address) __xip_unmap is looking for. To maintain XIP's established mappings correctly on MIPS, we need Nick's fix to mremap's move_one_page (originally presented as an optimization), to replace the ZERO_PAGE appropriate to the old address by the ZERO_PAGE appropriate to the new address. (But when I first saw this, I was thinking the ZERO_PAGEs themselves would get corrupted, very bad. Now I think it's the other way round, that the established mappings will fail to see the newly written data: incorrect, but not corrupting everything else. Whether filemap_xip's technique is generally safe, I'd hesitate to say in a hurry: it's interesting, but we've never tried to do that in tmpfs.) Signed-off-by: Hugh Dickins <> Signed-off-by: Nick Piggin <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
Diffstat (limited to 'mm')
1 files changed, 4 insertions, 0 deletions
diff --git a/mm/mremap.c b/mm/mremap.c
index fc45dc9a617b..a32fed454bd7 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -141,6 +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));
set_pte_at(mm, new_addr, dst, pte);
} else
error = -ENOMEM;