1 files changed, 11 insertions, 1 deletions

diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index 1d1b1e13f79f..6f32b2b1f76b 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -311,14 +311,24 @@ static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
         __young;                                                        \
 })
 
+/*
+ * set_pte_at_notify() sets the pte _after_ running the notifier.
+ * This is safe to start by updating the secondary MMUs, because the primary MMU
+ * pte invalidate must have already happened with a ptep_clear_flush() before
+ * set_pte_at_notify() has been invoked.  Updating the secondary MMUs first is
+ * required when we change both the protection of the mapping from read-only to
+ * read-write and the pfn (like during copy on write page faults). Otherwise the
+ * old page would remain mapped readonly in the secondary MMUs after the new
+ * page is already writable by some CPU through the primary MMU.
+ */
 #define set_pte_at_notify(__mm, __address, __ptep, __pte)               \
 ({                                                                      \
         struct mm_struct *___mm = __mm;                                 \
         unsigned long ___address = __address;                           \
         pte_t ___pte = __pte;                                           \
                                                                         \
-        set_pte_at(___mm, ___address, __ptep, ___pte);                  \
         mmu_notifier_change_pte(___mm, ___address, ___pte);             \
+        set_pte_at(___mm, ___address, __ptep, ___pte);                  \
 })
 
 #else /* CONFIG_MMU_NOTIFIER */