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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 /include/asm-generic
parent63a12d9d01831208a47f5c0fbbf93f503d1fb162 (diff)
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 'include/asm-generic')
-rw-r--r--include/asm-generic/pgtable.h14
1 files changed, 14 insertions, 0 deletions
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 081ff8826bf6..752e30d63904 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -253,6 +253,20 @@ static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)
#define pgprot_device pgprot_noncached
#endif
+#ifndef pgprot_modify
+#define pgprot_modify pgprot_modify
+static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
+{
+ if (pgprot_val(oldprot) == pgprot_val(pgprot_noncached(oldprot)))
+ newprot = pgprot_noncached(newprot);
+ if (pgprot_val(oldprot) == pgprot_val(pgprot_writecombine(oldprot)))
+ newprot = pgprot_writecombine(newprot);
+ if (pgprot_val(oldprot) == pgprot_val(pgprot_device(oldprot)))
+ newprot = pgprot_device(newprot);
+ return newprot;
+}
+#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