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authorPeter Feiner <pfeiner@google.com>2014-10-13 15:55:46 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-10-14 02:18:28 +0200
commit64e455079e1bd7787cc47be30b7f601ce682a5f6 (patch)
tree05193bd91be3ffc0d33ddd3ffb654ef4c23778f9 /mm/memory.c
parent63a12d9d01831208a47f5c0fbbf93f503d1fb162 (diff)
downloadlinux-64e455079e1bd7787cc47be30b7f601ce682a5f6.tar.bz2
mm: softdirty: enable write notifications on VMAs after VM_SOFTDIRTY cleared
For VMAs that don't want write notifications, PTEs created for read faults have their write bit set. If the read fault happens after VM_SOFTDIRTY is cleared, then the PTE's softdirty bit will remain clear after subsequent writes. Here's a simple code snippet to demonstrate the bug: char* m = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_SHARED, -1, 0); system("echo 4 > /proc/$PPID/clear_refs"); /* clear VM_SOFTDIRTY */ assert(*m == '\0'); /* new PTE allows write access */ assert(!soft_dirty(x)); *m = 'x'; /* should dirty the page */ assert(soft_dirty(x)); /* fails */ With this patch, write notifications are enabled when VM_SOFTDIRTY is cleared. Furthermore, to avoid unnecessary faults, write notifications are disabled when VM_SOFTDIRTY is set. As a side effect of enabling and disabling write notifications with care, this patch fixes a bug in mprotect where vm_page_prot bits set by drivers were zapped on mprotect. An analogous bug was fixed in mmap by commit c9d0bf241451 ("mm: uncached vma support with writenotify"). Signed-off-by: Peter Feiner <pfeiner@google.com> Reported-by: Peter Feiner <pfeiner@google.com> Suggested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Pavel Emelyanov <xemul@parallels.com> Cc: Jamie Liu <jamieliu@google.com> Cc: Hugh Dickins <hughd@google.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Bjorn Helgaas <bhelgaas@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memory.c')
-rw-r--r--mm/memory.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/memory.c b/mm/memory.c
index e229970e4223..1cc6bfbd872e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2053,7 +2053,8 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
old_page = vm_normal_page(vma, address, orig_pte);
if (!old_page) {
/*
- * VM_MIXEDMAP !pfn_valid() case
+ * VM_MIXEDMAP !pfn_valid() case, or VM_SOFTDIRTY clear on a
+ * VM_PFNMAP VMA.
*
* We should not cow pages in a shared writeable mapping.
* Just mark the pages writable as we can't do any dirty