[PATCH 0 of 3] mmu notifier v18

[PATCH 0 of 3] mmu notifier v18

[Andrea Arcangeli]

This splits the list.h changes in patch number 1, mm_take_all_locks patch 2,
and mmu-notifier-core becomes patch 3 as requested.

mm_take/drop_all_locks have been cleaned up as requested to move the bitflips
in proper methods outside the main vma loop.

[PATCH 0 of 3] mmu notifier v18

[Andrea Arcangeli]

This splits the list.h changes in patch number 1, mm_take_all_locks patch 2,
and mmu-notifier-core becomes patch 3 as requested.

mm_take/drop_all_locks have been cleaned up as requested to move the bitflips
in proper methods outside the main vma loop.

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[PATCH 0 of 3] mmu notifier v18

[Andrea Arcangeli]

This splits the list.h changes in patch number 1, mm_take_all_locks patch 2,
and mmu-notifier-core becomes patch 3 as requested.

mm_take/drop_all_locks have been cleaned up as requested to move the bitflips
in proper methods outside the main vma loop.

[PATCH 1 of 3] list_del_init_rcu

[Andrea Arcangeli]

From: Andrea Arcangeli <andrea@qumranet.com>

Introduces list_del_init_rcu and documents it (fixes a comment for
list_del_rcu too).

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff -r 86e3ce291996 -r becc195598f8 include/linux/list.h
--- a/include/linux/list.h	Wed Jun 04 10:35:03 2008 -0700
+++ b/include/linux/list.h	Thu Jun 05 17:30:14 2008 +0200
@@ -747,7 +747,7 @@ static inline void hlist_del(struct hlis
  * or hlist_del_rcu(), running on this same list.
  * However, it is perfectly legal to run concurrently with
  * the _rcu list-traversal primitives, such as
- * hlist_for_each_entry().
+ * hlist_for_each_entry_rcu().
  */
 static inline void hlist_del_rcu(struct hlist_node *n)
 {
@@ -760,6 +760,34 @@ static inline void hlist_del_init(struct
 	if (!hlist_unhashed(n)) {
 		__hlist_del(n);
 		INIT_HLIST_NODE(n);
+	}
+}
+
+/**
+ * hlist_del_init_rcu - deletes entry from hash list with re-initialization
+ * @n: the element to delete from the hash list.
+ *
+ * Note: list_unhashed() on the node return true after this. It is
+ * useful for RCU based read lockfree traversal if the writer side
+ * must know if the list entry is still hashed or already unhashed.
+ *
+ * In particular, it means that we can not poison the forward pointers
+ * that may still be used for walking the hash list and we can only
+ * zero the pprev pointer so list_unhashed() will return true after
+ * this.
+ *
+ * The caller must take whatever precautions are necessary (such as
+ * holding appropriate locks) to avoid racing with another
+ * list-mutation primitive, such as hlist_add_head_rcu() or
+ * hlist_del_rcu(), running on this same list.  However, it is
+ * perfectly legal to run concurrently with the _rcu list-traversal
+ * primitives, such as hlist_for_each_entry_rcu().
+ */
+static inline void hlist_del_init_rcu(struct hlist_node *n)
+{
+	if (!hlist_unhashed(n)) {
+		__hlist_del(n);
+		n->pprev = NULL;
 	}
 }
 

[PATCH 1 of 3] list_del_init_rcu

[Andrea Arcangeli, Andrea Arcangeli]

Introduces list_del_init_rcu and documents it (fixes a comment for
list_del_rcu too).

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff -r 86e3ce291996 -r becc195598f8 include/linux/list.h
--- a/include/linux/list.h	Wed Jun 04 10:35:03 2008 -0700
+++ b/include/linux/list.h	Thu Jun 05 17:30:14 2008 +0200
@@ -747,7 +747,7 @@ static inline void hlist_del(struct hlis
  * or hlist_del_rcu(), running on this same list.
  * However, it is perfectly legal to run concurrently with
  * the _rcu list-traversal primitives, such as
- * hlist_for_each_entry().
+ * hlist_for_each_entry_rcu().
  */
 static inline void hlist_del_rcu(struct hlist_node *n)
 {
@@ -760,6 +760,34 @@ static inline void hlist_del_init(struct
 	if (!hlist_unhashed(n)) {
 		__hlist_del(n);
 		INIT_HLIST_NODE(n);
+	}
+}
+
+/**
+ * hlist_del_init_rcu - deletes entry from hash list with re-initialization
+ * @n: the element to delete from the hash list.
+ *
+ * Note: list_unhashed() on the node return true after this. It is
+ * useful for RCU based read lockfree traversal if the writer side
+ * must know if the list entry is still hashed or already unhashed.
+ *
+ * In particular, it means that we can not poison the forward pointers
+ * that may still be used for walking the hash list and we can only
+ * zero the pprev pointer so list_unhashed() will return true after
+ * this.
+ *
+ * The caller must take whatever precautions are necessary (such as
+ * holding appropriate locks) to avoid racing with another
+ * list-mutation primitive, such as hlist_add_head_rcu() or
+ * hlist_del_rcu(), running on this same list.  However, it is
+ * perfectly legal to run concurrently with the _rcu list-traversal
+ * primitives, such as hlist_for_each_entry_rcu().
+ */
+static inline void hlist_del_init_rcu(struct hlist_node *n)
+{
+	if (!hlist_unhashed(n)) {
+		__hlist_del(n);
+		n->pprev = NULL;
 	}
 }
 

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[PATCH 1 of 3] list_del_init_rcu

[Andrea Arcangeli]

From: Andrea Arcangeli <andrea@qumranet.com>

Introduces list_del_init_rcu and documents it (fixes a comment for
list_del_rcu too).

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff -r 86e3ce291996 -r becc195598f8 include/linux/list.h
--- a/include/linux/list.h	Wed Jun 04 10:35:03 2008 -0700
+++ b/include/linux/list.h	Thu Jun 05 17:30:14 2008 +0200
@@ -747,7 +747,7 @@ static inline void hlist_del(struct hlis
  * or hlist_del_rcu(), running on this same list.
  * However, it is perfectly legal to run concurrently with
  * the _rcu list-traversal primitives, such as
- * hlist_for_each_entry().
+ * hlist_for_each_entry_rcu().
  */
 static inline void hlist_del_rcu(struct hlist_node *n)
 {
@@ -760,6 +760,34 @@ static inline void hlist_del_init(struct
 	if (!hlist_unhashed(n)) {
 		__hlist_del(n);
 		INIT_HLIST_NODE(n);
+	}
+}
+
+/**
+ * hlist_del_init_rcu - deletes entry from hash list with re-initialization
+ * @n: the element to delete from the hash list.
+ *
+ * Note: list_unhashed() on the node return true after this. It is
+ * useful for RCU based read lockfree traversal if the writer side
+ * must know if the list entry is still hashed or already unhashed.
+ *
+ * In particular, it means that we can not poison the forward pointers
+ * that may still be used for walking the hash list and we can only
+ * zero the pprev pointer so list_unhashed() will return true after
+ * this.
+ *
+ * The caller must take whatever precautions are necessary (such as
+ * holding appropriate locks) to avoid racing with another
+ * list-mutation primitive, such as hlist_add_head_rcu() or
+ * hlist_del_rcu(), running on this same list.  However, it is
+ * perfectly legal to run concurrently with the _rcu list-traversal
+ * primitives, such as hlist_for_each_entry_rcu().
+ */
+static inline void hlist_del_init_rcu(struct hlist_node *n)
+{
+	if (!hlist_unhashed(n)) {
+		__hlist_del(n);
+		n->pprev = NULL;
 	}
 }
 

[PATCH 2 of 3] mm_take_all_locks

[Andrea Arcangeli]

From: Andrea Arcangeli <andrea@qumranet.com>

mm_take_all_locks holds off reclaim from an entire mm_struct. This allows mmu
notifiers to register into the mm at any time with the guarantee that no mmu
operation is in progress on the mm.

This operation locks against the VM for all pte/vma/mm related operations that
could ever happen on a certain mm. This includes vmtruncate, try_to_unmap, and
all page faults.

The caller must take the mmap_sem in write mode before calling
mm_take_all_locks(). The caller isn't allowed to release the mmap_sem until
mm_drop_all_locks() returns.

mmap_sem in write mode is required in order to block all operations that could
modify pagetables and free pages without need of altering the vma layout (for
example populate_range() with nonlinear vmas). It's also needed in write mode
to avoid new anon_vmas to be associated with existing vmas.

A single task can't take more than one mm_take_all_locks() in a row or it would
deadlock.

mm_take_all_locks() and mm_drop_all_locks are expensive operations
that may have to take thousand of locks.

mm_take_all_locks() can fail if it's interrupted by signals.

When mmu_notifier_register returns, we must be sure that the driver is notified
if some task is in the middle of a vmtruncate for the 'mm' where the mmu
notifier was registered (mmu_notifier_invalidate_range_start/end is run around
the vmtruncation but mmu_notifier_register can run after
mmu_notifier_invalidate_range_start and before
mmu_notifier_invalidate_range_end). Same problem for rmap paths. And we've to
remove page pinning to avoid replicating the tlb_gather logic inside KVM (and
GRU doesn't work well with page pinning regardless of needing tlb_gather), so
without mm_take_all_locks when vmtruncate frees the page, kvm would have no way
to notice that it mapped into sptes a page that is going into the freelist
without a chance of any further mmu_notifier notification.

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff -r becc195598f8 -r 082f312bc682 include/linux/mm.h
--- a/include/linux/mm.h	Thu Jun 05 17:30:14 2008 +0200
+++ b/include/linux/mm.h	Thu Jun 05 17:30:17 2008 +0200
@@ -1067,6 +1067,9 @@ extern struct vm_area_struct *copy_vma(s
 	unsigned long addr, unsigned long len, pgoff_t pgoff);
 extern void exit_mmap(struct mm_struct *);
 
+extern int mm_take_all_locks(struct mm_struct *mm);
+extern void mm_drop_all_locks(struct mm_struct *mm);
+
 #ifdef CONFIG_PROC_FS
 /* From fs/proc/base.c. callers must _not_ hold the mm's exe_file_lock */
 extern void added_exe_file_vma(struct mm_struct *mm);
diff -r becc195598f8 -r 082f312bc682 include/linux/pagemap.h
--- a/include/linux/pagemap.h	Thu Jun 05 17:30:14 2008 +0200
+++ b/include/linux/pagemap.h	Thu Jun 05 17:30:17 2008 +0200
@@ -19,6 +19,7 @@
  */
 #define	AS_EIO		(__GFP_BITS_SHIFT + 0)	/* IO error on async write */
 #define AS_ENOSPC	(__GFP_BITS_SHIFT + 1)	/* ENOSPC on async write */
+#define AS_MM_ALL_LOCKS	(__GFP_BITS_SHIFT + 2)	/* under mm_take_all_locks() */
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
 {
diff -r becc195598f8 -r 082f312bc682 include/linux/rmap.h
--- a/include/linux/rmap.h	Thu Jun 05 17:30:14 2008 +0200
+++ b/include/linux/rmap.h	Thu Jun 05 17:30:17 2008 +0200
@@ -26,6 +26,14 @@
  */
 struct anon_vma {
 	spinlock_t lock;	/* Serialize access to vma list */
+	/*
+	 * NOTE: the LSB of the head.next is set by
+	 * mm_take_all_locks() _after_ taking the above lock. So the
+	 * head must only be read/written after taking the above lock
+	 * to be sure to see a valid next pointer. The LSB bit itself
+	 * is serialized by a system wide lock only visible to
+	 * mm_take_all_locks() (mm_all_locks_mutex).
+	 */
 	struct list_head head;	/* List of private "related" vmas */
 };
 
diff -r becc195598f8 -r 082f312bc682 mm/mmap.c
--- a/mm/mmap.c	Thu Jun 05 17:30:14 2008 +0200
+++ b/mm/mmap.c	Thu Jun 05 17:30:17 2008 +0200
@@ -2255,3 +2255,161 @@ int install_special_mapping(struct mm_st
 
 	return 0;
 }
+
+static DEFINE_MUTEX(mm_all_locks_mutex);
+
+static void vm_lock_anon_vma(struct anon_vma *anon_vma)
+{
+	if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) {
+		/*
+		 * The LSB of head.next can't change from under us
+		 * because we hold the global_mm_spinlock.
+		 */
+		spin_lock(&anon_vma->lock);
+		/*
+		 * We can safely modify head.next after taking the
+		 * anon_vma->lock. If some other vma in this mm shares
+		 * the same anon_vma we won't take it again.
+		 *
+		 * No need of atomic instructions here, head.next
+		 * can't change from under us thanks to the
+		 * anon_vma->lock.
+		 */
+		if (__test_and_set_bit(0, (unsigned long *)
+				       &anon_vma->head.next))
+			BUG();
+	}
+}
+
+static void vm_lock_mapping(struct address_space *mapping)
+{
+	if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
+		/*
+		 * AS_MM_ALL_LOCKS can't change from under us because
+		 * we hold the global_mm_spinlock.
+		 *
+		 * Operations on ->flags have to be atomic because
+		 * even if AS_MM_ALL_LOCKS is stable thanks to the
+		 * global_mm_spinlock, there may be other cpus
+		 * changing other bitflags in parallel to us.
+		 */
+		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
+			BUG();
+		spin_lock(&mapping->i_mmap_lock);
+	}
+}
+
+/*
+ * This operation locks against the VM for all pte/vma/mm related
+ * operations that could ever happen on a certain mm. This includes
+ * vmtruncate, try_to_unmap, and all page faults.
+ *
+ * The caller must take the mmap_sem in write mode before calling
+ * mm_take_all_locks(). The caller isn't allowed to release the
+ * mmap_sem until mm_drop_all_locks() returns.
+ *
+ * mmap_sem in write mode is required in order to block all operations
+ * that could modify pagetables and free pages without need of
+ * altering the vma layout (for example populate_range() with
+ * nonlinear vmas). It's also needed in write mode to avoid new
+ * anon_vmas to be associated with existing vmas.
+ *
+ * A single task can't take more than one mm_take_all_locks() in a row
+ * or it would deadlock.
+ *
+ * The LSB in anon_vma->head.next and the AS_MM_ALL_LOCKS bitflag in
+ * mapping->flags avoid to take the same lock twice, if more than one
+ * vma in this mm is backed by the same anon_vma or address_space.
+ *
+ * We can take all the locks in random order because the VM code
+ * taking i_mmap_lock or anon_vma->lock outside the mmap_sem never
+ * takes more than one of them in a row. Secondly we're protected
+ * against a concurrent mm_take_all_locks() by the mm_all_locks_mutex.
+ *
+ * mm_take_all_locks() and mm_drop_all_locks are expensive operations
+ * that may have to take thousand of locks.
+ *
+ * mm_take_all_locks() can fail if it's interrupted by signals.
+ */
+int mm_take_all_locks(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+	int ret = -EINTR;
+
+	BUG_ON(down_read_trylock(&mm->mmap_sem));
+
+	mutex_lock(&mm_all_locks_mutex);
+
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		if (signal_pending(current))
+			goto out_unlock;
+                if (vma->anon_vma)
+                        vm_lock_anon_vma(vma->anon_vma);
+                if (vma->vm_file && vma->vm_file->f_mapping)
+                        vm_lock_mapping(vma->vm_file->f_mapping);
+	}
+	ret = 0;
+
+out_unlock:
+	if (ret)
+		mm_drop_all_locks(mm);
+
+	return ret;
+}
+
+static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
+{
+	if (test_bit(0, (unsigned long *) &anon_vma->head.next)) {
+		/*
+		 * The LSB of head.next can't change to 0 from under
+		 * us because we hold the global_mm_spinlock.
+		 *
+		 * We must however clear the bitflag before unlocking
+		 * the vma so the users using the anon_vma->head will
+		 * never see our bitflag.
+		 *
+		 * No need of atomic instructions here, head.next
+		 * can't change from under us until we release the
+		 * anon_vma->lock.
+		 */
+		if (!__test_and_clear_bit(0, (unsigned long *)
+					  &anon_vma->head.next))
+			BUG();
+		spin_unlock(&anon_vma->lock);
+	}
+}
+
+static void vm_unlock_mapping(struct address_space *mapping)
+{
+	if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
+		/*
+		 * AS_MM_ALL_LOCKS can't change to 0 from under us
+		 * because we hold the global_mm_spinlock.
+		 */
+		spin_unlock(&mapping->i_mmap_lock);
+		if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
+					&mapping->flags))
+			BUG();
+	}
+}
+
+/*
+ * The mmap_sem cannot be released by the caller until
+ * mm_drop_all_locks() returns.
+ */
+void mm_drop_all_locks(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+
+	BUG_ON(down_read_trylock(&mm->mmap_sem));
+	BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));
+
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		if (vma->anon_vma)
+			vm_unlock_anon_vma(vma->anon_vma);
+		if (vma->vm_file && vma->vm_file->f_mapping)
+			vm_unlock_mapping(vma->vm_file->f_mapping);
+	}
+
+	mutex_unlock(&mm_all_locks_mutex);
+}

[PATCH 2 of 3] mm_take_all_locks

[Andrea Arcangeli, Andrea Arcangeli]

mm_take_all_locks holds off reclaim from an entire mm_struct. This allows mmu
notifiers to register into the mm at any time with the guarantee that no mmu
operation is in progress on the mm.

This operation locks against the VM for all pte/vma/mm related operations that
could ever happen on a certain mm. This includes vmtruncate, try_to_unmap, and
all page faults.

The caller must take the mmap_sem in write mode before calling
mm_take_all_locks(). The caller isn't allowed to release the mmap_sem until
mm_drop_all_locks() returns.

mmap_sem in write mode is required in order to block all operations that could
modify pagetables and free pages without need of altering the vma layout (for
example populate_range() with nonlinear vmas). It's also needed in write mode
to avoid new anon_vmas to be associated with existing vmas.

A single task can't take more than one mm_take_all_locks() in a row or it would
deadlock.

mm_take_all_locks() and mm_drop_all_locks are expensive operations
that may have to take thousand of locks.

mm_take_all_locks() can fail if it's interrupted by signals.

When mmu_notifier_register returns, we must be sure that the driver is notified
if some task is in the middle of a vmtruncate for the 'mm' where the mmu
notifier was registered (mmu_notifier_invalidate_range_start/end is run around
the vmtruncation but mmu_notifier_register can run after
mmu_notifier_invalidate_range_start and before
mmu_notifier_invalidate_range_end). Same problem for rmap paths. And we've to
remove page pinning to avoid replicating the tlb_gather logic inside KVM (and
GRU doesn't work well with page pinning regardless of needing tlb_gather), so
without mm_take_all_locks when vmtruncate frees the page, kvm would have no way
to notice that it mapped into sptes a page that is going into the freelist
without a chance of any further mmu_notifier notification.

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff -r becc195598f8 -r 082f312bc682 include/linux/mm.h
--- a/include/linux/mm.h	Thu Jun 05 17:30:14 2008 +0200
+++ b/include/linux/mm.h	Thu Jun 05 17:30:17 2008 +0200
@@ -1067,6 +1067,9 @@ extern struct vm_area_struct *copy_vma(s
 	unsigned long addr, unsigned long len, pgoff_t pgoff);
 extern void exit_mmap(struct mm_struct *);
 
+extern int mm_take_all_locks(struct mm_struct *mm);
+extern void mm_drop_all_locks(struct mm_struct *mm);
+
 #ifdef CONFIG_PROC_FS
 /* From fs/proc/base.c. callers must _not_ hold the mm's exe_file_lock */
 extern void added_exe_file_vma(struct mm_struct *mm);
diff -r becc195598f8 -r 082f312bc682 include/linux/pagemap.h
--- a/include/linux/pagemap.h	Thu Jun 05 17:30:14 2008 +0200
+++ b/include/linux/pagemap.h	Thu Jun 05 17:30:17 2008 +0200
@@ -19,6 +19,7 @@
  */
 #define	AS_EIO		(__GFP_BITS_SHIFT + 0)	/* IO error on async write */
 #define AS_ENOSPC	(__GFP_BITS_SHIFT + 1)	/* ENOSPC on async write */
+#define AS_MM_ALL_LOCKS	(__GFP_BITS_SHIFT + 2)	/* under mm_take_all_locks() */
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
 {
diff -r becc195598f8 -r 082f312bc682 include/linux/rmap.h
--- a/include/linux/rmap.h	Thu Jun 05 17:30:14 2008 +0200
+++ b/include/linux/rmap.h	Thu Jun 05 17:30:17 2008 +0200
@@ -26,6 +26,14 @@
  */
 struct anon_vma {
 	spinlock_t lock;	/* Serialize access to vma list */
+	/*
+	 * NOTE: the LSB of the head.next is set by
+	 * mm_take_all_locks() _after_ taking the above lock. So the
+	 * head must only be read/written after taking the above lock
+	 * to be sure to see a valid next pointer. The LSB bit itself
+	 * is serialized by a system wide lock only visible to
+	 * mm_take_all_locks() (mm_all_locks_mutex).
+	 */
 	struct list_head head;	/* List of private "related" vmas */
 };
 
diff -r becc195598f8 -r 082f312bc682 mm/mmap.c
--- a/mm/mmap.c	Thu Jun 05 17:30:14 2008 +0200
+++ b/mm/mmap.c	Thu Jun 05 17:30:17 2008 +0200
@@ -2255,3 +2255,161 @@ int install_special_mapping(struct mm_st
 
 	return 0;
 }
+
+static DEFINE_MUTEX(mm_all_locks_mutex);
+
+static void vm_lock_anon_vma(struct anon_vma *anon_vma)
+{
+	if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) {
+		/*
+		 * The LSB of head.next can't change from under us
+		 * because we hold the global_mm_spinlock.
+		 */
+		spin_lock(&anon_vma->lock);
+		/*
+		 * We can safely modify head.next after taking the
+		 * anon_vma->lock. If some other vma in this mm shares
+		 * the same anon_vma we won't take it again.
+		 *
+		 * No need of atomic instructions here, head.next
+		 * can't change from under us thanks to the
+		 * anon_vma->lock.
+		 */
+		if (__test_and_set_bit(0, (unsigned long *)
+				       &anon_vma->head.next))
+			BUG();
+	}
+}
+
+static void vm_lock_mapping(struct address_space *mapping)
+{
+	if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
+		/*
+		 * AS_MM_ALL_LOCKS can't change from under us because
+		 * we hold the global_mm_spinlock.
+		 *
+		 * Operations on ->flags have to be atomic because
+		 * even if AS_MM_ALL_LOCKS is stable thanks to the
+		 * global_mm_spinlock, there may be other cpus
+		 * changing other bitflags in parallel to us.
+		 */
+		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
+			BUG();
+		spin_lock(&mapping->i_mmap_lock);
+	}
+}
+
+/*
+ * This operation locks against the VM for all pte/vma/mm related
+ * operations that could ever happen on a certain mm. This includes
+ * vmtruncate, try_to_unmap, and all page faults.
+ *
+ * The caller must take the mmap_sem in write mode before calling
+ * mm_take_all_locks(). The caller isn't allowed to release the
+ * mmap_sem until mm_drop_all_locks() returns.
+ *
+ * mmap_sem in write mode is required in order to block all operations
+ * that could modify pagetables and free pages without need of
+ * altering the vma layout (for example populate_range() with
+ * nonlinear vmas). It's also needed in write mode to avoid new
+ * anon_vmas to be associated with existing vmas.
+ *
+ * A single task can't take more than one mm_take_all_locks() in a row
+ * or it would deadlock.
+ *
+ * The LSB in anon_vma->head.next and the AS_MM_ALL_LOCKS bitflag in
+ * mapping->flags avoid to take the same lock twice, if more than one
+ * vma in this mm is backed by the same anon_vma or address_space.
+ *
+ * We can take all the locks in random order because the VM code
+ * taking i_mmap_lock or anon_vma->lock outside the mmap_sem never
+ * takes more than one of them in a row. Secondly we're protected
+ * against a concurrent mm_take_all_locks() by the mm_all_locks_mutex.
+ *
+ * mm_take_all_locks() and mm_drop_all_locks are expensive operations
+ * that may have to take thousand of locks.
+ *
+ * mm_take_all_locks() can fail if it's interrupted by signals.
+ */
+int mm_take_all_locks(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+	int ret = -EINTR;
+
+	BUG_ON(down_read_trylock(&mm->mmap_sem));
+
+	mutex_lock(&mm_all_locks_mutex);
+
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		if (signal_pending(current))
+			goto out_unlock;
+                if (vma->anon_vma)
+                        vm_lock_anon_vma(vma->anon_vma);
+                if (vma->vm_file && vma->vm_file->f_mapping)
+                        vm_lock_mapping(vma->vm_file->f_mapping);
+	}
+	ret = 0;
+
+out_unlock:
+	if (ret)
+		mm_drop_all_locks(mm);
+
+	return ret;
+}
+
+static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
+{
+	if (test_bit(0, (unsigned long *) &anon_vma->head.next)) {
+		/*
+		 * The LSB of head.next can't change to 0 from under
+		 * us because we hold the global_mm_spinlock.
+		 *
+		 * We must however clear the bitflag before unlocking
+		 * the vma so the users using the anon_vma->head will
+		 * never see our bitflag.
+		 *
+		 * No need of atomic instructions here, head.next
+		 * can't change from under us until we release the
+		 * anon_vma->lock.
+		 */
+		if (!__test_and_clear_bit(0, (unsigned long *)
+					  &anon_vma->head.next))
+			BUG();
+		spin_unlock(&anon_vma->lock);
+	}
+}
+
+static void vm_unlock_mapping(struct address_space *mapping)
+{
+	if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
+		/*
+		 * AS_MM_ALL_LOCKS can't change to 0 from under us
+		 * because we hold the global_mm_spinlock.
+		 */
+		spin_unlock(&mapping->i_mmap_lock);
+		if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
+					&mapping->flags))
+			BUG();
+	}
+}
+
+/*
+ * The mmap_sem cannot be released by the caller until
+ * mm_drop_all_locks() returns.
+ */
+void mm_drop_all_locks(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+
+	BUG_ON(down_read_trylock(&mm->mmap_sem));
+	BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));
+
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		if (vma->anon_vma)
+			vm_unlock_anon_vma(vma->anon_vma);
+		if (vma->vm_file && vma->vm_file->f_mapping)
+			vm_unlock_mapping(vma->vm_file->f_mapping);
+	}
+
+	mutex_unlock(&mm_all_locks_mutex);
+}

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[PATCH 2 of 3] mm_take_all_locks

[Andrea Arcangeli]

From: Andrea Arcangeli <andrea@qumranet.com>

mm_take_all_locks holds off reclaim from an entire mm_struct. This allows mmu
notifiers to register into the mm at any time with the guarantee that no mmu
operation is in progress on the mm.

This operation locks against the VM for all pte/vma/mm related operations that
could ever happen on a certain mm. This includes vmtruncate, try_to_unmap, and
all page faults.

The caller must take the mmap_sem in write mode before calling
mm_take_all_locks(). The caller isn't allowed to release the mmap_sem until
mm_drop_all_locks() returns.

mmap_sem in write mode is required in order to block all operations that could
modify pagetables and free pages without need of altering the vma layout (for
example populate_range() with nonlinear vmas). It's also needed in write mode
to avoid new anon_vmas to be associated with existing vmas.

A single task can't take more than one mm_take_all_locks() in a row or it would
deadlock.

mm_take_all_locks() and mm_drop_all_locks are expensive operations
that may have to take thousand of locks.

mm_take_all_locks() can fail if it's interrupted by signals.

When mmu_notifier_register returns, we must be sure that the driver is notified
if some task is in the middle of a vmtruncate for the 'mm' where the mmu
notifier was registered (mmu_notifier_invalidate_range_start/end is run around
the vmtruncation but mmu_notifier_register can run after
mmu_notifier_invalidate_range_start and before
mmu_notifier_invalidate_range_end). Same problem for rmap paths. And we've to
remove page pinning to avoid replicating the tlb_gather logic inside KVM (and
GRU doesn't work well with page pinning regardless of needing tlb_gather), so
without mm_take_all_locks when vmtruncate frees the page, kvm would have no way
to notice that it mapped into sptes a page that is going into the freelist
without a chance of any further mmu_notifier notification.

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff -r becc195598f8 -r 082f312bc682 include/linux/mm.h
--- a/include/linux/mm.h	Thu Jun 05 17:30:14 2008 +0200
+++ b/include/linux/mm.h	Thu Jun 05 17:30:17 2008 +0200
@@ -1067,6 +1067,9 @@ extern struct vm_area_struct *copy_vma(s
 	unsigned long addr, unsigned long len, pgoff_t pgoff);
 extern void exit_mmap(struct mm_struct *);
 
+extern int mm_take_all_locks(struct mm_struct *mm);
+extern void mm_drop_all_locks(struct mm_struct *mm);
+
 #ifdef CONFIG_PROC_FS
 /* From fs/proc/base.c. callers must _not_ hold the mm's exe_file_lock */
 extern void added_exe_file_vma(struct mm_struct *mm);
diff -r becc195598f8 -r 082f312bc682 include/linux/pagemap.h
--- a/include/linux/pagemap.h	Thu Jun 05 17:30:14 2008 +0200
+++ b/include/linux/pagemap.h	Thu Jun 05 17:30:17 2008 +0200
@@ -19,6 +19,7 @@
  */
 #define	AS_EIO		(__GFP_BITS_SHIFT + 0)	/* IO error on async write */
 #define AS_ENOSPC	(__GFP_BITS_SHIFT + 1)	/* ENOSPC on async write */
+#define AS_MM_ALL_LOCKS	(__GFP_BITS_SHIFT + 2)	/* under mm_take_all_locks() */
 
 static inline void mapping_set_error(struct address_space *mapping, int error)
 {
diff -r becc195598f8 -r 082f312bc682 include/linux/rmap.h
--- a/include/linux/rmap.h	Thu Jun 05 17:30:14 2008 +0200
+++ b/include/linux/rmap.h	Thu Jun 05 17:30:17 2008 +0200
@@ -26,6 +26,14 @@
  */
 struct anon_vma {
 	spinlock_t lock;	/* Serialize access to vma list */
+	/*
+	 * NOTE: the LSB of the head.next is set by
+	 * mm_take_all_locks() _after_ taking the above lock. So the
+	 * head must only be read/written after taking the above lock
+	 * to be sure to see a valid next pointer. The LSB bit itself
+	 * is serialized by a system wide lock only visible to
+	 * mm_take_all_locks() (mm_all_locks_mutex).
+	 */
 	struct list_head head;	/* List of private "related" vmas */
 };
 
diff -r becc195598f8 -r 082f312bc682 mm/mmap.c
--- a/mm/mmap.c	Thu Jun 05 17:30:14 2008 +0200
+++ b/mm/mmap.c	Thu Jun 05 17:30:17 2008 +0200
@@ -2255,3 +2255,161 @@ int install_special_mapping(struct mm_st
 
 	return 0;
 }
+
+static DEFINE_MUTEX(mm_all_locks_mutex);
+
+static void vm_lock_anon_vma(struct anon_vma *anon_vma)
+{
+	if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) {
+		/*
+		 * The LSB of head.next can't change from under us
+		 * because we hold the global_mm_spinlock.
+		 */
+		spin_lock(&anon_vma->lock);
+		/*
+		 * We can safely modify head.next after taking the
+		 * anon_vma->lock. If some other vma in this mm shares
+		 * the same anon_vma we won't take it again.
+		 *
+		 * No need of atomic instructions here, head.next
+		 * can't change from under us thanks to the
+		 * anon_vma->lock.
+		 */
+		if (__test_and_set_bit(0, (unsigned long *)
+				       &anon_vma->head.next))
+			BUG();
+	}
+}
+
+static void vm_lock_mapping(struct address_space *mapping)
+{
+	if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
+		/*
+		 * AS_MM_ALL_LOCKS can't change from under us because
+		 * we hold the global_mm_spinlock.
+		 *
+		 * Operations on ->flags have to be atomic because
+		 * even if AS_MM_ALL_LOCKS is stable thanks to the
+		 * global_mm_spinlock, there may be other cpus
+		 * changing other bitflags in parallel to us.
+		 */
+		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
+			BUG();
+		spin_lock(&mapping->i_mmap_lock);
+	}
+}
+
+/*
+ * This operation locks against the VM for all pte/vma/mm related
+ * operations that could ever happen on a certain mm. This includes
+ * vmtruncate, try_to_unmap, and all page faults.
+ *
+ * The caller must take the mmap_sem in write mode before calling
+ * mm_take_all_locks(). The caller isn't allowed to release the
+ * mmap_sem until mm_drop_all_locks() returns.
+ *
+ * mmap_sem in write mode is required in order to block all operations
+ * that could modify pagetables and free pages without need of
+ * altering the vma layout (for example populate_range() with
+ * nonlinear vmas). It's also needed in write mode to avoid new
+ * anon_vmas to be associated with existing vmas.
+ *
+ * A single task can't take more than one mm_take_all_locks() in a row
+ * or it would deadlock.
+ *
+ * The LSB in anon_vma->head.next and the AS_MM_ALL_LOCKS bitflag in
+ * mapping->flags avoid to take the same lock twice, if more than one
+ * vma in this mm is backed by the same anon_vma or address_space.
+ *
+ * We can take all the locks in random order because the VM code
+ * taking i_mmap_lock or anon_vma->lock outside the mmap_sem never
+ * takes more than one of them in a row. Secondly we're protected
+ * against a concurrent mm_take_all_locks() by the mm_all_locks_mutex.
+ *
+ * mm_take_all_locks() and mm_drop_all_locks are expensive operations
+ * that may have to take thousand of locks.
+ *
+ * mm_take_all_locks() can fail if it's interrupted by signals.
+ */
+int mm_take_all_locks(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+	int ret = -EINTR;
+
+	BUG_ON(down_read_trylock(&mm->mmap_sem));
+
+	mutex_lock(&mm_all_locks_mutex);
+
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		if (signal_pending(current))
+			goto out_unlock;
+                if (vma->anon_vma)
+                        vm_lock_anon_vma(vma->anon_vma);
+                if (vma->vm_file && vma->vm_file->f_mapping)
+                        vm_lock_mapping(vma->vm_file->f_mapping);
+	}
+	ret = 0;
+
+out_unlock:
+	if (ret)
+		mm_drop_all_locks(mm);
+
+	return ret;
+}
+
+static void vm_unlock_anon_vma(struct anon_vma *anon_vma)
+{
+	if (test_bit(0, (unsigned long *) &anon_vma->head.next)) {
+		/*
+		 * The LSB of head.next can't change to 0 from under
+		 * us because we hold the global_mm_spinlock.
+		 *
+		 * We must however clear the bitflag before unlocking
+		 * the vma so the users using the anon_vma->head will
+		 * never see our bitflag.
+		 *
+		 * No need of atomic instructions here, head.next
+		 * can't change from under us until we release the
+		 * anon_vma->lock.
+		 */
+		if (!__test_and_clear_bit(0, (unsigned long *)
+					  &anon_vma->head.next))
+			BUG();
+		spin_unlock(&anon_vma->lock);
+	}
+}
+
+static void vm_unlock_mapping(struct address_space *mapping)
+{
+	if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
+		/*
+		 * AS_MM_ALL_LOCKS can't change to 0 from under us
+		 * because we hold the global_mm_spinlock.
+		 */
+		spin_unlock(&mapping->i_mmap_lock);
+		if (!test_and_clear_bit(AS_MM_ALL_LOCKS,
+					&mapping->flags))
+			BUG();
+	}
+}
+
+/*
+ * The mmap_sem cannot be released by the caller until
+ * mm_drop_all_locks() returns.
+ */
+void mm_drop_all_locks(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+
+	BUG_ON(down_read_trylock(&mm->mmap_sem));
+	BUG_ON(!mutex_is_locked(&mm_all_locks_mutex));
+
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		if (vma->anon_vma)
+			vm_unlock_anon_vma(vma->anon_vma);
+		if (vma->vm_file && vma->vm_file->f_mapping)
+			vm_unlock_mapping(vma->vm_file->f_mapping);
+	}
+
+	mutex_unlock(&mm_all_locks_mutex);
+}

Re: [PATCH 2 of 3] mm_take_all_locks

[Linus Torvalds]

Just a small comment fix.

On Thu, 5 Jun 2008, Andrea Arcangeli wrote:
> +		/*
> +		 * AS_MM_ALL_LOCKS can't change from under us because
> +		 * we hold the global_mm_spinlock.

There's no global_mm_spinlock, you mean the 'mm_all_locks_mutex'.

(There was at least one other case where you had that comment issue).

		Linus

Re: [PATCH 2 of 3] mm_take_all_locks

[Linus Torvalds]

Just a small comment fix.

On Thu, 5 Jun 2008, Andrea Arcangeli wrote:
> +		/*
> +		 * AS_MM_ALL_LOCKS can't change from under us because
> +		 * we hold the global_mm_spinlock.

There's no global_mm_spinlock, you mean the 'mm_all_locks_mutex'.

(There was at least one other case where you had that comment issue).

		Linus

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Re: [PATCH 2 of 3] mm_take_all_locks

[Andrea Arcangeli]

On Thu, Jun 05, 2008 at 09:15:41AM -0700, Linus Torvalds wrote:
> 
> Just a small comment fix.
> 
> On Thu, 5 Jun 2008, Andrea Arcangeli wrote:
> > +		/*
> > +		 * AS_MM_ALL_LOCKS can't change from under us because
> > +		 * we hold the global_mm_spinlock.
> 
> There's no global_mm_spinlock, you mean the 'mm_all_locks_mutex'.
> 
> (There was at least one other case where you had that comment issue).

From: Andrea Arcangeli <andrea@qumranet.com>

Indeed, I meant mm_all_locks_mutex, this will fix it, or if you prefer
a resubmit of the 2/3 let me know. Thanks!

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
---

diff -r 082f312bc682 mm/mmap.c
--- a/mm/mmap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mmap.c	Thu Jun 05 18:40:23 2008 +0200
@@ -2263,7 +2263,7 @@ static void vm_lock_anon_vma(struct anon
 	if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) {
 		/*
 		 * The LSB of head.next can't change from under us
-		 * because we hold the global_mm_spinlock.
+		 * because we hold the mm_all_locks_mutex.
 		 */
 		spin_lock(&anon_vma->lock);
 		/*
@@ -2286,11 +2286,11 @@ static void vm_lock_mapping(struct addre
 	if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
 		/*
 		 * AS_MM_ALL_LOCKS can't change from under us because
-		 * we hold the global_mm_spinlock.
+		 * we hold the mm_all_locks_mutex.
 		 *
 		 * Operations on ->flags have to be atomic because
 		 * even if AS_MM_ALL_LOCKS is stable thanks to the
-		 * global_mm_spinlock, there may be other cpus
+		 * mm_all_locks_mutex, there may be other cpus
 		 * changing other bitflags in parallel to us.
 		 */
 		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
@@ -2362,7 +2362,7 @@ static void vm_unlock_anon_vma(struct an
 	if (test_bit(0, (unsigned long *) &anon_vma->head.next)) {
 		/*
 		 * The LSB of head.next can't change to 0 from under
-		 * us because we hold the global_mm_spinlock.
+		 * us because we hold the mm_all_locks_mutex.
 		 *
 		 * We must however clear the bitflag before unlocking
 		 * the vma so the users using the anon_vma->head will
@@ -2384,7 +2384,7 @@ static void vm_unlock_mapping(struct add
 	if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
 		/*
 		 * AS_MM_ALL_LOCKS can't change to 0 from under us
-		 * because we hold the global_mm_spinlock.
+		 * because we hold the mm_all_locks_mutex.
 		 */
 		spin_unlock(&mapping->i_mmap_lock);
 		if (!test_and_clear_bit(AS_MM_ALL_LOCKS,

Re: [PATCH 2 of 3] mm_take_all_locks

[Andrea Arcangeli]

On Thu, Jun 05, 2008 at 09:15:41AM -0700, Linus Torvalds wrote:
> 
> Just a small comment fix.
> 
> On Thu, 5 Jun 2008, Andrea Arcangeli wrote:
> > +		/*
> > +		 * AS_MM_ALL_LOCKS can't change from under us because
> > +		 * we hold the global_mm_spinlock.
> 
> There's no global_mm_spinlock, you mean the 'mm_all_locks_mutex'.
> 
> (There was at least one other case where you had that comment issue).

From: Andrea Arcangeli <andrea@qumranet.com>

Indeed, I meant mm_all_locks_mutex, this will fix it, or if you prefer
a resubmit of the 2/3 let me know. Thanks!

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
---

diff -r 082f312bc682 mm/mmap.c
--- a/mm/mmap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mmap.c	Thu Jun 05 18:40:23 2008 +0200
@@ -2263,7 +2263,7 @@ static void vm_lock_anon_vma(struct anon
 	if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) {
 		/*
 		 * The LSB of head.next can't change from under us
-		 * because we hold the global_mm_spinlock.
+		 * because we hold the mm_all_locks_mutex.
 		 */
 		spin_lock(&anon_vma->lock);
 		/*
@@ -2286,11 +2286,11 @@ static void vm_lock_mapping(struct addre
 	if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
 		/*
 		 * AS_MM_ALL_LOCKS can't change from under us because
-		 * we hold the global_mm_spinlock.
+		 * we hold the mm_all_locks_mutex.
 		 *
 		 * Operations on ->flags have to be atomic because
 		 * even if AS_MM_ALL_LOCKS is stable thanks to the
-		 * global_mm_spinlock, there may be other cpus
+		 * mm_all_locks_mutex, there may be other cpus
 		 * changing other bitflags in parallel to us.
 		 */
 		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
@@ -2362,7 +2362,7 @@ static void vm_unlock_anon_vma(struct an
 	if (test_bit(0, (unsigned long *) &anon_vma->head.next)) {
 		/*
 		 * The LSB of head.next can't change to 0 from under
-		 * us because we hold the global_mm_spinlock.
+		 * us because we hold the mm_all_locks_mutex.
 		 *
 		 * We must however clear the bitflag before unlocking
 		 * the vma so the users using the anon_vma->head will
@@ -2384,7 +2384,7 @@ static void vm_unlock_mapping(struct add
 	if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
 		/*
 		 * AS_MM_ALL_LOCKS can't change to 0 from under us
-		 * because we hold the global_mm_spinlock.
+		 * because we hold the mm_all_locks_mutex.
 		 */
 		spin_unlock(&mapping->i_mmap_lock);
 		if (!test_and_clear_bit(AS_MM_ALL_LOCKS,

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[ofa-general] Re: [PATCH 2 of 3] mm_take_all_locks

[Andrea Arcangeli]

On Thu, Jun 05, 2008 at 09:15:41AM -0700, Linus Torvalds wrote:
> 
> Just a small comment fix.
> 
> On Thu, 5 Jun 2008, Andrea Arcangeli wrote:
> > +		/*
> > +		 * AS_MM_ALL_LOCKS can't change from under us because
> > +		 * we hold the global_mm_spinlock.
> 
> There's no global_mm_spinlock, you mean the 'mm_all_locks_mutex'.
> 
> (There was at least one other case where you had that comment issue).

From: Andrea Arcangeli <andrea@qumranet.com>

Indeed, I meant mm_all_locks_mutex, this will fix it, or if you prefer
a resubmit of the 2/3 let me know. Thanks!

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
---

diff -r 082f312bc682 mm/mmap.c
--- a/mm/mmap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mmap.c	Thu Jun 05 18:40:23 2008 +0200
@@ -2263,7 +2263,7 @@ static void vm_lock_anon_vma(struct anon
 	if (!test_bit(0, (unsigned long *) &anon_vma->head.next)) {
 		/*
 		 * The LSB of head.next can't change from under us
-		 * because we hold the global_mm_spinlock.
+		 * because we hold the mm_all_locks_mutex.
 		 */
 		spin_lock(&anon_vma->lock);
 		/*
@@ -2286,11 +2286,11 @@ static void vm_lock_mapping(struct addre
 	if (!test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
 		/*
 		 * AS_MM_ALL_LOCKS can't change from under us because
-		 * we hold the global_mm_spinlock.
+		 * we hold the mm_all_locks_mutex.
 		 *
 		 * Operations on ->flags have to be atomic because
 		 * even if AS_MM_ALL_LOCKS is stable thanks to the
-		 * global_mm_spinlock, there may be other cpus
+		 * mm_all_locks_mutex, there may be other cpus
 		 * changing other bitflags in parallel to us.
 		 */
 		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
@@ -2362,7 +2362,7 @@ static void vm_unlock_anon_vma(struct an
 	if (test_bit(0, (unsigned long *) &anon_vma->head.next)) {
 		/*
 		 * The LSB of head.next can't change to 0 from under
-		 * us because we hold the global_mm_spinlock.
+		 * us because we hold the mm_all_locks_mutex.
 		 *
 		 * We must however clear the bitflag before unlocking
 		 * the vma so the users using the anon_vma->head will
@@ -2384,7 +2384,7 @@ static void vm_unlock_mapping(struct add
 	if (test_bit(AS_MM_ALL_LOCKS, &mapping->flags)) {
 		/*
 		 * AS_MM_ALL_LOCKS can't change to 0 from under us
-		 * because we hold the global_mm_spinlock.
+		 * because we hold the mm_all_locks_mutex.
 		 */
 		spin_unlock(&mapping->i_mmap_lock);
 		if (!test_and_clear_bit(AS_MM_ALL_LOCKS,

[PATCH 3 of 3] mmu-notifier-core

[Andrea Arcangeli]

From: Andrea Arcangeli <andrea@qumranet.com>

With KVM/GFP/XPMEM there isn't just the primary CPU MMU pointing to
pages. There are secondary MMUs (with secondary sptes and secondary
tlbs) too. sptes in the kvm case are shadow pagetables, but when I say
spte in mmu-notifier context, I mean "secondary pte". In GRU case
there's no actual secondary pte and there's only a secondary tlb
because the GRU secondary MMU has no knowledge about sptes and every
secondary tlb miss event in the MMU always generates a page fault that
has to be resolved by the CPU (this is not the case of KVM where the a
secondary tlb miss will walk sptes in hardware and it will refill the
secondary tlb transparently to software if the corresponding spte is
present). The same way zap_page_range has to invalidate the pte before
freeing the page, the spte (and secondary tlb) must also be
invalidated before any page is freed and reused.

Currently we take a page_count pin on every page mapped by sptes, but
that means the pages can't be swapped whenever they're mapped by any
spte because they're part of the guest working set. Furthermore a spte
unmap event can immediately lead to a page to be freed when the pin is
released (so requiring the same complex and relatively slow tlb_gather
smp safe logic we have in zap_page_range and that can be avoided
completely if the spte unmap event doesn't require an unpin of the
page previously mapped in the secondary MMU).

The mmu notifiers allow kvm/GRU/XPMEM to attach to the tsk->mm and
know when the VM is swapping or freeing or doing anything on the
primary MMU so that the secondary MMU code can drop sptes before the
pages are freed, avoiding all page pinning and allowing 100% reliable
swapping of guest physical address space. Furthermore it avoids the
code that teardown the mappings of the secondary MMU, to implement a
logic like tlb_gather in zap_page_range that would require many IPI to
flush other cpu tlbs, for each fixed number of spte unmapped.

To make an example: if what happens on the primary MMU is a protection
downgrade (from writeable to wrprotect) the secondary MMU mappings
will be invalidated, and the next secondary-mmu-page-fault will call
get_user_pages and trigger a do_wp_page through get_user_pages if it
called get_user_pages with write=1, and it'll re-establishing an
updated spte or secondary-tlb-mapping on the copied page. Or it will
setup a readonly spte or readonly tlb mapping if it's a guest-read, if
it calls get_user_pages with write=0. This is just an example.

This allows to map any page pointed by any pte (and in turn visible in
the primary CPU MMU), into a secondary MMU (be it a pure tlb like GRU,
or an full MMU with both sptes and secondary-tlb like the
shadow-pagetable layer with kvm), or a remote DMA in software like
XPMEM (hence needing of schedule in XPMEM code to send the invalidate
to the remote node, while no need to schedule in kvm/gru as it's an
immediate event like invalidating primary-mmu pte).

At least for KVM without this patch it's impossible to swap guests
reliably. And having this feature and removing the page pin allows
several other optimizations that simplify life considerably.

Dependencies:

1) mm_take_all_locks() to register the mmu notifier when the whole VM
   isn't doing anything with "mm". This allows mmu notifier users to
   keep track if the VM is in the middle of the
   invalidate_range_begin/end critical section with an atomic counter
   incraese in range_begin and decreased in range_end. No secondary
   MMU page fault is allowed to map any spte or secondary tlb
   reference, while the VM is in the middle of range_begin/end as any
   page returned by get_user_pages in that critical section could
   later immediately be freed without any further ->invalidate_page
   notification (invalidate_range_begin/end works on ranges and
   ->invalidate_page isn't called immediately before freeing the
   page). To stop all page freeing and pagetable overwrites the
   mmap_sem must be taken in write mode and all other anon_vma/i_mmap
   locks must be taken too.

2) It'd be a waste to add branches in the VM if nobody could possibly
   run KVM/GRU/XPMEM on the kernel, so mmu notifiers will only enabled
   if CONFIG_KVM=m/y. In the current kernel kvm won't yet take
   advantage of mmu notifiers, but this already allows to compile a
   KVM external module against a kernel with mmu notifiers enabled and
   from the next pull from kvm.git we'll start using them. And
   GRU/XPMEM will also be able to continue the development by enabling
   KVM=m in their config, until they submit all GRU/XPMEM GPLv2 code
   to the mainline kernel. Then they can also enable MMU_NOTIFIERS in
   the same way KVM does it (even if KVM=n). This guarantees nobody
   selects MMU_NOTIFIER=y if KVM and GRU and XPMEM are all =n.

The mmu_notifier_register call can fail because mm_take_all_locks may
be interrupted by a signal and return -EINTR. Because
mmu_notifier_reigster is used when a driver startup, a failure can be
gracefully handled. Here an example of the change applied to kvm to
register the mmu notifiers. Usually when a driver startups other
allocations are required anyway and -ENOMEM failure paths exists
already.

 struct  kvm *kvm_arch_create_vm(void)
 {
        struct kvm *kvm = kzalloc(sizeof(struct kvm), GFP_KERNEL);
+       int err;

        if (!kvm)
                return ERR_PTR(-ENOMEM);

        INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);

+       kvm->arch.mmu_notifier.ops = &kvm_mmu_notifier_ops;
+       err = mmu_notifier_register(&kvm->arch.mmu_notifier, current->mm);
+       if (err) {
+               kfree(kvm);
+               return ERR_PTR(err);
+       }
+
        return kvm;
 }

mmu_notifier_unregister returns void and it's reliable.

The patch also adds a few needed but missing includes that would prevent kernel
to compile after these changes on non-x86 archs (x86 didn't need them by luck).

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---

diff -r 082f312bc682 -r 9cf86778092b arch/x86/kvm/Kconfig
--- a/arch/x86/kvm/Kconfig	Thu Jun 05 17:30:17 2008 +0200
+++ b/arch/x86/kvm/Kconfig	Thu Jun 05 17:31:21 2008 +0200
@@ -21,6 +21,7 @@ config KVM
 	tristate "Kernel-based Virtual Machine (KVM) support"
 	depends on HAVE_KVM
 	select PREEMPT_NOTIFIERS
+	select MMU_NOTIFIER
 	select ANON_INODES
 	---help---
 	  Support hosting fully virtualized guest machines using hardware
diff -r 082f312bc682 -r 9cf86778092b include/linux/mm_types.h
--- a/include/linux/mm_types.h	Thu Jun 05 17:30:17 2008 +0200
+++ b/include/linux/mm_types.h	Thu Jun 05 17:31:21 2008 +0200
@@ -10,6 +10,7 @@
 #include <linux/rbtree.h>
 #include <linux/rwsem.h>
 #include <linux/completion.h>
+#include <linux/cpumask.h>
 #include <asm/page.h>
 #include <asm/mmu.h>
 
@@ -244,6 +245,9 @@ struct mm_struct {
 	struct file *exe_file;
 	unsigned long num_exe_file_vmas;
 #endif
+#ifdef CONFIG_MMU_NOTIFIER
+	struct mmu_notifier_mm *mmu_notifier_mm;
+#endif
 };
 
 #endif /* _LINUX_MM_TYPES_H */
diff -r 082f312bc682 -r 9cf86778092b include/linux/mmu_notifier.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/include/linux/mmu_notifier.h	Thu Jun 05 17:31:21 2008 +0200
@@ -0,0 +1,279 @@
+#ifndef _LINUX_MMU_NOTIFIER_H
+#define _LINUX_MMU_NOTIFIER_H
+
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/mm_types.h>
+
+struct mmu_notifier;
+struct mmu_notifier_ops;
+
+#ifdef CONFIG_MMU_NOTIFIER
+
+/*
+ * The mmu notifier_mm structure is allocated and installed in
+ * mm->mmu_notifier_mm inside the mm_take_all_locks() protected
+ * critical section and it's released only when mm_count reaches zero
+ * in mmdrop().
+ */
+struct mmu_notifier_mm {
+	/* all mmu notifiers registerd in this mm are queued in this list */
+	struct hlist_head list;
+	/* to serialize the list modifications and hlist_unhashed */
+	spinlock_t lock;
+};
+
+struct mmu_notifier_ops {
+	/*
+	 * Called either by mmu_notifier_unregister or when the mm is
+	 * being destroyed by exit_mmap, always before all pages are
+	 * freed. This can run concurrently with other mmu notifier
+	 * methods (the ones invoked outside the mm context) and it
+	 * should tear down all secondary mmu mappings and freeze the
+	 * secondary mmu. If this method isn't implemented you've to
+	 * be sure that nothing could possibly write to the pages
+	 * through the secondary mmu by the time the last thread with
+	 * tsk->mm == mm exits.
+	 *
+	 * As side note: the pages freed after ->release returns could
+	 * be immediately reallocated by the gart at an alias physical
+	 * address with a different cache model, so if ->release isn't
+	 * implemented because all _software_ driven memory accesses
+	 * through the secondary mmu are terminated by the time the
+	 * last thread of this mm quits, you've also to be sure that
+	 * speculative _hardware_ operations can't allocate dirty
+	 * cachelines in the cpu that could not be snooped and made
+	 * coherent with the other read and write operations happening
+	 * through the gart alias address, so leading to memory
+	 * corruption.
+	 */
+	void (*release)(struct mmu_notifier *mn,
+			struct mm_struct *mm);
+
+	/*
+	 * clear_flush_young is called after the VM is
+	 * test-and-clearing the young/accessed bitflag in the
+	 * pte. This way the VM will provide proper aging to the
+	 * accesses to the page through the secondary MMUs and not
+	 * only to the ones through the Linux pte.
+	 */
+	int (*clear_flush_young)(struct mmu_notifier *mn,
+				 struct mm_struct *mm,
+				 unsigned long address);
+
+	/*
+	 * Before this is invoked any secondary MMU is still ok to
+	 * read/write to the page previously pointed to by the Linux
+	 * pte because the page hasn't been freed yet and it won't be
+	 * freed until this returns. If required set_page_dirty has to
+	 * be called internally to this method.
+	 */
+	void (*invalidate_page)(struct mmu_notifier *mn,
+				struct mm_struct *mm,
+				unsigned long address);
+
+	/*
+	 * invalidate_range_start() and invalidate_range_end() must be
+	 * paired and are called only when the mmap_sem and/or the
+	 * locks protecting the reverse maps are held. The subsystem
+	 * must guarantee that no additional references are taken to
+	 * the pages in the range established between the call to
+	 * invalidate_range_start() and the matching call to
+	 * invalidate_range_end().
+	 *
+	 * Invalidation of multiple concurrent ranges may be
+	 * optionally permitted by the driver. Either way the
+	 * establishment of sptes is forbidden in the range passed to
+	 * invalidate_range_begin/end for the whole duration of the
+	 * invalidate_range_begin/end critical section.
+	 *
+	 * invalidate_range_start() is called when all pages in the
+	 * range are still mapped and have at least a refcount of one.
+	 *
+	 * invalidate_range_end() is called when all pages in the
+	 * range have been unmapped and the pages have been freed by
+	 * the VM.
+	 *
+	 * The VM will remove the page table entries and potentially
+	 * the page between invalidate_range_start() and
+	 * invalidate_range_end(). If the page must not be freed
+	 * because of pending I/O or other circumstances then the
+	 * invalidate_range_start() callback (or the initial mapping
+	 * by the driver) must make sure that the refcount is kept
+	 * elevated.
+	 *
+	 * If the driver increases the refcount when the pages are
+	 * initially mapped into an address space then either
+	 * invalidate_range_start() or invalidate_range_end() may
+	 * decrease the refcount. If the refcount is decreased on
+	 * invalidate_range_start() then the VM can free pages as page
+	 * table entries are removed.  If the refcount is only
+	 * droppped on invalidate_range_end() then the driver itself
+	 * will drop the last refcount but it must take care to flush
+	 * any secondary tlb before doing the final free on the
+	 * page. Pages will no longer be referenced by the linux
+	 * address space but may still be referenced by sptes until
+	 * the last refcount is dropped.
+	 */
+	void (*invalidate_range_start)(struct mmu_notifier *mn,
+				       struct mm_struct *mm,
+				       unsigned long start, unsigned long end);
+	void (*invalidate_range_end)(struct mmu_notifier *mn,
+				     struct mm_struct *mm,
+				     unsigned long start, unsigned long end);
+};
+
+/*
+ * The notifier chains are protected by mmap_sem and/or the reverse map
+ * semaphores. Notifier chains are only changed when all reverse maps and
+ * the mmap_sem locks are taken.
+ *
+ * Therefore notifier chains can only be traversed when either
+ *
+ * 1. mmap_sem is held.
+ * 2. One of the reverse map locks is held (i_mmap_lock or anon_vma->lock).
+ * 3. No other concurrent thread can access the list (release)
+ */
+struct mmu_notifier {
+	struct hlist_node hlist;
+	const struct mmu_notifier_ops *ops;
+};
+
+static inline int mm_has_notifiers(struct mm_struct *mm)
+{
+	return unlikely(mm->mmu_notifier_mm);
+}
+
+extern int mmu_notifier_register(struct mmu_notifier *mn,
+				 struct mm_struct *mm);
+extern int __mmu_notifier_register(struct mmu_notifier *mn,
+				   struct mm_struct *mm);
+extern void mmu_notifier_unregister(struct mmu_notifier *mn,
+				    struct mm_struct *mm);
+extern void __mmu_notifier_mm_destroy(struct mm_struct *mm);
+extern void __mmu_notifier_release(struct mm_struct *mm);
+extern int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					  unsigned long address);
+extern void __mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address);
+extern void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end);
+extern void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end);
+
+static inline void mmu_notifier_release(struct mm_struct *mm)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_release(mm);
+}
+
+static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					  unsigned long address)
+{
+	if (mm_has_notifiers(mm))
+		return __mmu_notifier_clear_flush_young(mm, address);
+	return 0;
+}
+
+static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_invalidate_page(mm, address);
+}
+
+static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_invalidate_range_start(mm, start, end);
+}
+
+static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_invalidate_range_end(mm, start, end);
+}
+
+static inline void mmu_notifier_mm_init(struct mm_struct *mm)
+{
+	mm->mmu_notifier_mm = NULL;
+}
+
+static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_mm_destroy(mm);
+}
+
+/*
+ * These two macros will sometime replace ptep_clear_flush.
+ * ptep_clear_flush is impleemnted as macro itself, so this also is
+ * implemented as a macro until ptep_clear_flush will converted to an
+ * inline function, to diminish the risk of compilation failure. The
+ * invalidate_page method over time can be moved outside the PT lock
+ * and these two macros can be later removed.
+ */
+#define ptep_clear_flush_notify(__vma, __address, __ptep)		\
+({									\
+	pte_t __pte;							\
+	struct vm_area_struct *___vma = __vma;				\
+	unsigned long ___address = __address;				\
+	__pte = ptep_clear_flush(___vma, ___address, __ptep);		\
+	mmu_notifier_invalidate_page(___vma->vm_mm, ___address);	\
+	__pte;								\
+})
+
+#define ptep_clear_flush_young_notify(__vma, __address, __ptep)		\
+({									\
+	int __young;							\
+	struct vm_area_struct *___vma = __vma;				\
+	unsigned long ___address = __address;				\
+	__young = ptep_clear_flush_young(___vma, ___address, __ptep);	\
+	__young |= mmu_notifier_clear_flush_young(___vma->vm_mm,	\
+						  ___address);		\
+	__young;							\
+})
+
+#else /* CONFIG_MMU_NOTIFIER */
+
+static inline void mmu_notifier_release(struct mm_struct *mm)
+{
+}
+
+static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					  unsigned long address)
+{
+	return 0;
+}
+
+static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address)
+{
+}
+
+static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+}
+
+static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+}
+
+static inline void mmu_notifier_mm_init(struct mm_struct *mm)
+{
+}
+
+static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
+{
+}
+
+#define ptep_clear_flush_young_notify ptep_clear_flush_young
+#define ptep_clear_flush_notify ptep_clear_flush
+
+#endif /* CONFIG_MMU_NOTIFIER */
+
+#endif /* _LINUX_MMU_NOTIFIER_H */
diff -r 082f312bc682 -r 9cf86778092b kernel/fork.c
--- a/kernel/fork.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/kernel/fork.c	Thu Jun 05 17:31:21 2008 +0200
@@ -54,6 +54,7 @@
 #include <linux/tty.h>
 #include <linux/proc_fs.h>
 #include <linux/blkdev.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -386,6 +387,7 @@ static struct mm_struct * mm_init(struct
 
 	if (likely(!mm_alloc_pgd(mm))) {
 		mm->def_flags = 0;
+		mmu_notifier_mm_init(mm);
 		return mm;
 	}
 
@@ -418,6 +420,7 @@ void __mmdrop(struct mm_struct *mm)
 	BUG_ON(mm == &init_mm);
 	mm_free_pgd(mm);
 	destroy_context(mm);
+	mmu_notifier_mm_destroy(mm);
 	free_mm(mm);
 }
 EXPORT_SYMBOL_GPL(__mmdrop);
diff -r 082f312bc682 -r 9cf86778092b mm/Kconfig
--- a/mm/Kconfig	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/Kconfig	Thu Jun 05 17:31:21 2008 +0200
@@ -205,3 +205,6 @@ config VIRT_TO_BUS
 config VIRT_TO_BUS
 	def_bool y
 	depends on !ARCH_NO_VIRT_TO_BUS
+
+config MMU_NOTIFIER
+	bool
diff -r 082f312bc682 -r 9cf86778092b mm/Makefile
--- a/mm/Makefile	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/Makefile	Thu Jun 05 17:31:21 2008 +0200
@@ -33,4 +33,5 @@ obj-$(CONFIG_SMP) += allocpercpu.o
 obj-$(CONFIG_SMP) += allocpercpu.o
 obj-$(CONFIG_QUICKLIST) += quicklist.o
 obj-$(CONFIG_CGROUP_MEM_RES_CTLR) += memcontrol.o
+obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
 
diff -r 082f312bc682 -r 9cf86778092b mm/filemap_xip.c
--- a/mm/filemap_xip.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/filemap_xip.c	Thu Jun 05 17:31:21 2008 +0200
@@ -188,7 +188,7 @@ __xip_unmap (struct address_space * mapp
 		if (pte) {
 			/* Nuke the page table entry. */
 			flush_cache_page(vma, address, pte_pfn(*pte));
-			pteval = ptep_clear_flush(vma, address, pte);
+			pteval = ptep_clear_flush_notify(vma, address, pte);
 			page_remove_rmap(page, vma);
 			dec_mm_counter(mm, file_rss);
 			BUG_ON(pte_dirty(pteval));
diff -r 082f312bc682 -r 9cf86778092b mm/fremap.c
--- a/mm/fremap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/fremap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -15,6 +15,7 @@
 #include <linux/rmap.h>
 #include <linux/module.h>
 #include <linux/syscalls.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/mmu_context.h>
 #include <asm/cacheflush.h>
@@ -214,7 +215,9 @@ asmlinkage long sys_remap_file_pages(uns
 		spin_unlock(&mapping->i_mmap_lock);
 	}
 
+	mmu_notifier_invalidate_range_start(mm, start, start + size);
 	err = populate_range(mm, vma, start, size, pgoff);
+	mmu_notifier_invalidate_range_end(mm, start, start + size);
 	if (!err && !(flags & MAP_NONBLOCK)) {
 		if (unlikely(has_write_lock)) {
 			downgrade_write(&mm->mmap_sem);
diff -r 082f312bc682 -r 9cf86778092b mm/hugetlb.c
--- a/mm/hugetlb.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/hugetlb.c	Thu Jun 05 17:31:21 2008 +0200
@@ -14,6 +14,7 @@
 #include <linux/mempolicy.h>
 #include <linux/cpuset.h>
 #include <linux/mutex.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/page.h>
 #include <asm/pgtable.h>
@@ -823,6 +824,7 @@ void __unmap_hugepage_range(struct vm_ar
 	BUG_ON(start & ~HPAGE_MASK);
 	BUG_ON(end & ~HPAGE_MASK);
 
+	mmu_notifier_invalidate_range_start(mm, start, end);
 	spin_lock(&mm->page_table_lock);
 	for (address = start; address < end; address += HPAGE_SIZE) {
 		ptep = huge_pte_offset(mm, address);
@@ -843,6 +845,7 @@ void __unmap_hugepage_range(struct vm_ar
 	}
 	spin_unlock(&mm->page_table_lock);
 	flush_tlb_range(vma, start, end);
+	mmu_notifier_invalidate_range_end(mm, start, end);
 	list_for_each_entry_safe(page, tmp, &page_list, lru) {
 		list_del(&page->lru);
 		put_page(page);
diff -r 082f312bc682 -r 9cf86778092b mm/memory.c
--- a/mm/memory.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/memory.c	Thu Jun 05 17:31:21 2008 +0200
@@ -51,6 +51,7 @@
 #include <linux/init.h>
 #include <linux/writeback.h>
 #include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/pgalloc.h>
 #include <asm/uaccess.h>
@@ -649,6 +650,7 @@ int copy_page_range(struct mm_struct *ds
 	unsigned long next;
 	unsigned long addr = vma->vm_start;
 	unsigned long end = vma->vm_end;
+	int ret;
 
 	/*
 	 * Don't copy ptes where a page fault will fill them correctly.
@@ -664,17 +666,33 @@ int copy_page_range(struct mm_struct *ds
 	if (is_vm_hugetlb_page(vma))
 		return copy_hugetlb_page_range(dst_mm, src_mm, vma);
 
+	/*
+	 * We need to invalidate the secondary MMU mappings only when
+	 * there could be a permission downgrade on the ptes of the
+	 * parent mm. And a permission downgrade will only happen if
+	 * is_cow_mapping() returns true.
+	 */
+	if (is_cow_mapping(vma->vm_flags))
+		mmu_notifier_invalidate_range_start(src_mm, addr, end);
+
+	ret = 0;
 	dst_pgd = pgd_offset(dst_mm, addr);
 	src_pgd = pgd_offset(src_mm, addr);
 	do {
 		next = pgd_addr_end(addr, end);
 		if (pgd_none_or_clear_bad(src_pgd))
 			continue;
-		if (copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
-						vma, addr, next))
-			return -ENOMEM;
+		if (unlikely(copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
+					    vma, addr, next))) {
+			ret = -ENOMEM;
+			break;
+		}
 	} while (dst_pgd++, src_pgd++, addr = next, addr != end);
-	return 0;
+
+	if (is_cow_mapping(vma->vm_flags))
+		mmu_notifier_invalidate_range_end(src_mm,
+						  vma->vm_start, end);
+	return ret;
 }
 
 static unsigned long zap_pte_range(struct mmu_gather *tlb,
@@ -878,7 +896,9 @@ unsigned long unmap_vmas(struct mmu_gath
 	unsigned long start = start_addr;
 	spinlock_t *i_mmap_lock = details? details->i_mmap_lock: NULL;
 	int fullmm = (*tlbp)->fullmm;
+	struct mm_struct *mm = vma->vm_mm;
 
+	mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
 	for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next) {
 		unsigned long end;
 
@@ -929,6 +949,7 @@ unsigned long unmap_vmas(struct mmu_gath
 		}
 	}
 out:
+	mmu_notifier_invalidate_range_end(mm, start_addr, end_addr);
 	return start;	/* which is now the end (or restart) address */
 }
 
@@ -1561,10 +1582,11 @@ int apply_to_page_range(struct mm_struct
 {
 	pgd_t *pgd;
 	unsigned long next;
-	unsigned long end = addr + size;
+	unsigned long start = addr, end = addr + size;
 	int err;
 
 	BUG_ON(addr >= end);
+	mmu_notifier_invalidate_range_start(mm, start, end);
 	pgd = pgd_offset(mm, addr);
 	do {
 		next = pgd_addr_end(addr, end);
@@ -1572,6 +1594,7 @@ int apply_to_page_range(struct mm_struct
 		if (err)
 			break;
 	} while (pgd++, addr = next, addr != end);
+	mmu_notifier_invalidate_range_end(mm, start, end);
 	return err;
 }
 EXPORT_SYMBOL_GPL(apply_to_page_range);
@@ -1773,7 +1796,7 @@ gotten:
 		 * seen in the presence of one thread doing SMC and another
 		 * thread doing COW.
 		 */
-		ptep_clear_flush(vma, address, page_table);
+		ptep_clear_flush_notify(vma, address, page_table);
 		set_pte_at(mm, address, page_table, entry);
 		update_mmu_cache(vma, address, entry);
 		lru_cache_add_active(new_page);
diff -r 082f312bc682 -r 9cf86778092b mm/mmap.c
--- a/mm/mmap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mmap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -26,6 +26,7 @@
 #include <linux/mount.h>
 #include <linux/mempolicy.h>
 #include <linux/rmap.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
@@ -2048,6 +2049,7 @@ void exit_mmap(struct mm_struct *mm)
 
 	/* mm's last user has gone, and its about to be pulled down */
 	arch_exit_mmap(mm);
+	mmu_notifier_release(mm);
 
 	lru_add_drain();
 	flush_cache_mm(mm);
diff -r 082f312bc682 -r 9cf86778092b mm/mmu_notifier.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mm/mmu_notifier.c	Thu Jun 05 17:31:21 2008 +0200
@@ -0,0 +1,276 @@
+/*
+ *  linux/mm/mmu_notifier.c
+ *
+ *  Copyright (C) 2008  Qumranet, Inc.
+ *  Copyright (C) 2008  SGI
+ *             Christoph Lameter <clameter@sgi.com>
+ *
+ *  This work is licensed under the terms of the GNU GPL, version 2. See
+ *  the COPYING file in the top-level directory.
+ */
+
+#include <linux/mmu_notifier.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/err.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+
+/*
+ * This function can't run concurrently against mmu_notifier_register
+ * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
+ * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
+ * in parallel despite there being no task using this mm any more,
+ * through the vmas outside of the exit_mmap context, such as with
+ * vmtruncate. This serializes against mmu_notifier_unregister with
+ * the mmu_notifier_mm->lock in addition to RCU and it serializes
+ * against the other mmu notifiers with RCU. struct mmu_notifier_mm
+ * can't go away from under us as exit_mmap holds an mm_count pin
+ * itself.
+ */
+void __mmu_notifier_release(struct mm_struct *mm)
+{
+	struct mmu_notifier *mn;
+
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
+		mn = hlist_entry(mm->mmu_notifier_mm->list.first,
+				 struct mmu_notifier,
+				 hlist);
+		/*
+		 * We arrived before mmu_notifier_unregister so
+		 * mmu_notifier_unregister will do nothing other than
+		 * to wait ->release to finish and
+		 * mmu_notifier_unregister to return.
+		 */
+		hlist_del_init_rcu(&mn->hlist);
+		/*
+		 * RCU here will block mmu_notifier_unregister until
+		 * ->release returns.
+		 */
+		rcu_read_lock();
+		spin_unlock(&mm->mmu_notifier_mm->lock);
+		/*
+		 * if ->release runs before mmu_notifier_unregister it
+		 * must be handled as it's the only way for the driver
+		 * to flush all existing sptes and stop the driver
+		 * from establishing any more sptes before all the
+		 * pages in the mm are freed.
+		 */
+		if (mn->ops->release)
+			mn->ops->release(mn, mm);
+		rcu_read_unlock();
+		spin_lock(&mm->mmu_notifier_mm->lock);
+	}
+	spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	/*
+	 * synchronize_rcu here prevents mmu_notifier_release to
+	 * return to exit_mmap (which would proceed freeing all pages
+	 * in the mm) until the ->release method returns, if it was
+	 * invoked by mmu_notifier_unregister.
+	 *
+	 * The mmu_notifier_mm can't go away from under us because one
+	 * mm_count is hold by exit_mmap.
+	 */
+	synchronize_rcu();
+}
+
+/*
+ * If no young bitflag is supported by the hardware, ->clear_flush_young can
+ * unmap the address and return 1 or 0 depending if the mapping previously
+ * existed or not.
+ */
+int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					unsigned long address)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+	int young = 0;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->clear_flush_young)
+			young |= mn->ops->clear_flush_young(mn, mm, address);
+	}
+	rcu_read_unlock();
+
+	return young;
+}
+
+void __mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->invalidate_page)
+			mn->ops->invalidate_page(mn, mm, address);
+	}
+	rcu_read_unlock();
+}
+
+void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->invalidate_range_start)
+			mn->ops->invalidate_range_start(mn, mm, start, end);
+	}
+	rcu_read_unlock();
+}
+
+void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->invalidate_range_end)
+			mn->ops->invalidate_range_end(mn, mm, start, end);
+	}
+	rcu_read_unlock();
+}
+
+static int do_mmu_notifier_register(struct mmu_notifier *mn,
+				    struct mm_struct *mm,
+				    int take_mmap_sem)
+{
+	struct mmu_notifier_mm * mmu_notifier_mm;
+	int ret;
+
+	BUG_ON(atomic_read(&mm->mm_users) <= 0);
+
+	ret = -ENOMEM;
+	mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
+	if (unlikely(!mmu_notifier_mm))
+		goto out;
+
+	if (take_mmap_sem)
+		down_write(&mm->mmap_sem);
+	ret = mm_take_all_locks(mm);
+	if (unlikely(ret))
+		goto out_cleanup;
+
+	if (!mm_has_notifiers(mm)) {
+		INIT_HLIST_HEAD(&mmu_notifier_mm->list);
+		spin_lock_init(&mmu_notifier_mm->lock);
+		mm->mmu_notifier_mm = mmu_notifier_mm;
+		mmu_notifier_mm = NULL;
+	}
+	atomic_inc(&mm->mm_count);
+
+	/*
+	 * Serialize the update against mmu_notifier_unregister. A
+	 * side note: mmu_notifier_release can't run concurrently with
+	 * us because we hold the mm_users pin (either implicitly as
+	 * current->mm or explicitly with get_task_mm() or similar).
+	 * We can't race against any other mmu notifier method either
+	 * thanks to mm_take_all_locks().
+	 */
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
+	spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	mm_drop_all_locks(mm);
+out_cleanup:
+	if (take_mmap_sem)
+		up_write(&mm->mmap_sem);
+	/* kfree() does nothing if mmu_notifier_mm is NULL */
+	kfree(mmu_notifier_mm);
+out:
+	BUG_ON(atomic_read(&mm->mm_users) <= 0);
+	return ret;
+}
+
+/*
+ * Must not hold mmap_sem nor any other VM related lock when calling
+ * this registration function. Must also ensure mm_users can't go down
+ * to zero while this runs to avoid races with mmu_notifier_release,
+ * so mm has to be current->mm or the mm should be pinned safely such
+ * as with get_task_mm(). If the mm is not current->mm, the mm_users
+ * pin should be released by calling mmput after mmu_notifier_register
+ * returns. mmu_notifier_unregister must be always called to
+ * unregister the notifier. mm_count is automatically pinned to allow
+ * mmu_notifier_unregister to safely run at any time later, before or
+ * after exit_mmap. ->release will always be called before exit_mmap
+ * frees the pages.
+ */
+int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	return do_mmu_notifier_register(mn, mm, 1);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_register);
+
+/*
+ * Same as mmu_notifier_register but here the caller must hold the
+ * mmap_sem in write mode.
+ */
+int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	return do_mmu_notifier_register(mn, mm, 0);
+}
+EXPORT_SYMBOL_GPL(__mmu_notifier_register);
+
+/* this is called after the last mmu_notifier_unregister() returned */
+void __mmu_notifier_mm_destroy(struct mm_struct *mm)
+{
+	BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
+	kfree(mm->mmu_notifier_mm);
+	mm->mmu_notifier_mm = LIST_POISON1; /* debug */
+}
+
+/*
+ * This releases the mm_count pin automatically and frees the mm
+ * structure if it was the last user of it. It serializes against
+ * running mmu notifiers with RCU and against mmu_notifier_unregister
+ * with the unregister lock + RCU. All sptes must be dropped before
+ * calling mmu_notifier_unregister. ->release or any other notifier
+ * method may be invoked concurrently with mmu_notifier_unregister,
+ * and only after mmu_notifier_unregister returned we're guaranteed
+ * that ->release or any other method can't run anymore.
+ */
+void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	BUG_ON(atomic_read(&mm->mm_count) <= 0);
+
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	if (!hlist_unhashed(&mn->hlist)) {
+		hlist_del_rcu(&mn->hlist);
+
+		/*
+		 * RCU here will force exit_mmap to wait ->release to finish
+		 * before freeing the pages.
+		 */
+		rcu_read_lock();
+		spin_unlock(&mm->mmu_notifier_mm->lock);
+		/*
+		 * exit_mmap will block in mmu_notifier_release to
+		 * guarantee ->release is called before freeing the
+		 * pages.
+		 */
+		if (mn->ops->release)
+			mn->ops->release(mn, mm);
+		rcu_read_unlock();
+	} else
+		spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	/*
+	 * Wait any running method to finish, of course including
+	 * ->release if it was run by mmu_notifier_relase instead of us.
+	 */
+	synchronize_rcu();
+
+	BUG_ON(atomic_read(&mm->mm_count) <= 0);
+
+	mmdrop(mm);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
diff -r 082f312bc682 -r 9cf86778092b mm/mprotect.c
--- a/mm/mprotect.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mprotect.c	Thu Jun 05 17:31:21 2008 +0200
@@ -21,6 +21,7 @@
 #include <linux/syscalls.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
+#include <linux/mmu_notifier.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
 #include <asm/cacheflush.h>
@@ -207,10 +208,12 @@ success:
 		dirty_accountable = 1;
 	}
 
+	mmu_notifier_invalidate_range_start(mm, start, end);
 	if (is_vm_hugetlb_page(vma))
 		hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 	else
 		change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
+	mmu_notifier_invalidate_range_end(mm, start, end);
 	vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 	vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 	return 0;
diff -r 082f312bc682 -r 9cf86778092b mm/mremap.c
--- a/mm/mremap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mremap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -18,6 +18,7 @@
 #include <linux/highmem.h>
 #include <linux/security.h>
 #include <linux/syscalls.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
@@ -74,7 +75,11 @@ static void move_ptes(struct vm_area_str
 	struct mm_struct *mm = vma->vm_mm;
 	pte_t *old_pte, *new_pte, pte;
 	spinlock_t *old_ptl, *new_ptl;
+	unsigned long old_start;
 
+	old_start = old_addr;
+	mmu_notifier_invalidate_range_start(vma->vm_mm,
+					    old_start, old_end);
 	if (vma->vm_file) {
 		/*
 		 * Subtle point from Rajesh Venkatasubramanian: before
@@ -116,6 +121,7 @@ static void move_ptes(struct vm_area_str
 	pte_unmap_unlock(old_pte - 1, old_ptl);
 	if (mapping)
 		spin_unlock(&mapping->i_mmap_lock);
+	mmu_notifier_invalidate_range_end(vma->vm_mm, old_start, old_end);
 }
 
 #define LATENCY_LIMIT	(64 * PAGE_SIZE)
diff -r 082f312bc682 -r 9cf86778092b mm/rmap.c
--- a/mm/rmap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/rmap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -49,6 +49,7 @@
 #include <linux/module.h>
 #include <linux/kallsyms.h>
 #include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/tlbflush.h>
 
@@ -287,7 +288,7 @@ static int page_referenced_one(struct pa
 	if (vma->vm_flags & VM_LOCKED) {
 		referenced++;
 		*mapcount = 1;	/* break early from loop */
-	} else if (ptep_clear_flush_young(vma, address, pte))
+	} else if (ptep_clear_flush_young_notify(vma, address, pte))
 		referenced++;
 
 	/* Pretend the page is referenced if the task has the
@@ -457,7 +458,7 @@ static int page_mkclean_one(struct page 
 		pte_t entry;
 
 		flush_cache_page(vma, address, pte_pfn(*pte));
-		entry = ptep_clear_flush(vma, address, pte);
+		entry = ptep_clear_flush_notify(vma, address, pte);
 		entry = pte_wrprotect(entry);
 		entry = pte_mkclean(entry);
 		set_pte_at(mm, address, pte, entry);
@@ -717,14 +718,14 @@ static int try_to_unmap_one(struct page 
 	 * skipped over this mm) then we should reactivate it.
 	 */
 	if (!migration && ((vma->vm_flags & VM_LOCKED) ||
-			(ptep_clear_flush_young(vma, address, pte)))) {
+			(ptep_clear_flush_young_notify(vma, address, pte)))) {
 		ret = SWAP_FAIL;
 		goto out_unmap;
 	}
 
 	/* Nuke the page table entry. */
 	flush_cache_page(vma, address, page_to_pfn(page));
-	pteval = ptep_clear_flush(vma, address, pte);
+	pteval = ptep_clear_flush_notify(vma, address, pte);
 
 	/* Move the dirty bit to the physical page now the pte is gone. */
 	if (pte_dirty(pteval))
@@ -849,12 +850,12 @@ static void try_to_unmap_cluster(unsigne
 		page = vm_normal_page(vma, address, *pte);
 		BUG_ON(!page || PageAnon(page));
 
-		if (ptep_clear_flush_young(vma, address, pte))
+		if (ptep_clear_flush_young_notify(vma, address, pte))
 			continue;
 
 		/* Nuke the page table entry. */
 		flush_cache_page(vma, address, pte_pfn(*pte));
-		pteval = ptep_clear_flush(vma, address, pte);
+		pteval = ptep_clear_flush_notify(vma, address, pte);
 
 		/* If nonlinear, store the file page offset in the pte. */
 		if (page->index != linear_page_index(vma, address))

[PATCH 3 of 3] mmu-notifier-core

[Andrea Arcangeli, Andrea Arcangeli]

With KVM/GFP/XPMEM there isn't just the primary CPU MMU pointing to
pages. There are secondary MMUs (with secondary sptes and secondary
tlbs) too. sptes in the kvm case are shadow pagetables, but when I say
spte in mmu-notifier context, I mean "secondary pte". In GRU case
there's no actual secondary pte and there's only a secondary tlb
because the GRU secondary MMU has no knowledge about sptes and every
secondary tlb miss event in the MMU always generates a page fault that
has to be resolved by the CPU (this is not the case of KVM where the a
secondary tlb miss will walk sptes in hardware and it will refill the
secondary tlb transparently to software if the corresponding spte is
present). The same way zap_page_range has to invalidate the pte before
freeing the page, the spte (and secondary tlb) must also be
invalidated before any page is freed and reused.

Currently we take a page_count pin on every page mapped by sptes, but
that means the pages can't be swapped whenever they're mapped by any
spte because they're part of the guest working set. Furthermore a spte
unmap event can immediately lead to a page to be freed when the pin is
released (so requiring the same complex and relatively slow tlb_gather
smp safe logic we have in zap_page_range and that can be avoided
completely if the spte unmap event doesn't require an unpin of the
page previously mapped in the secondary MMU).

The mmu notifiers allow kvm/GRU/XPMEM to attach to the tsk->mm and
know when the VM is swapping or freeing or doing anything on the
primary MMU so that the secondary MMU code can drop sptes before the
pages are freed, avoiding all page pinning and allowing 100% reliable
swapping of guest physical address space. Furthermore it avoids the
code that teardown the mappings of the secondary MMU, to implement a
logic like tlb_gather in zap_page_range that would require many IPI to
flush other cpu tlbs, for each fixed number of spte unmapped.

To make an example: if what happens on the primary MMU is a protection
downgrade (from writeable to wrprotect) the secondary MMU mappings
will be invalidated, and the next secondary-mmu-page-fault will call
get_user_pages and trigger a do_wp_page through get_user_pages if it
called get_user_pages with write=1, and it'll re-establishing an
updated spte or secondary-tlb-mapping on the copied page. Or it will
setup a readonly spte or readonly tlb mapping if it's a guest-read, if
it calls get_user_pages with write=0. This is just an example.

This allows to map any page pointed by any pte (and in turn visible in
the primary CPU MMU), into a secondary MMU (be it a pure tlb like GRU,
or an full MMU with both sptes and secondary-tlb like the
shadow-pagetable layer with kvm), or a remote DMA in software like
XPMEM (hence needing of schedule in XPMEM code to send the invalidate
to the remote node, while no need to schedule in kvm/gru as it's an
immediate event like invalidating primary-mmu pte).

At least for KVM without this patch it's impossible to swap guests
reliably. And having this feature and removing the page pin allows
several other optimizations that simplify life considerably.

Dependencies:

1) mm_take_all_locks() to register the mmu notifier when the whole VM
   isn't doing anything with "mm". This allows mmu notifier users to
   keep track if the VM is in the middle of the
   invalidate_range_begin/end critical section with an atomic counter
   incraese in range_begin and decreased in range_end. No secondary
   MMU page fault is allowed to map any spte or secondary tlb
   reference, while the VM is in the middle of range_begin/end as any
   page returned by get_user_pages in that critical section could
   later immediately be freed without any further ->invalidate_page
   notification (invalidate_range_begin/end works on ranges and
   ->invalidate_page isn't called immediately before freeing the
   page). To stop all page freeing and pagetable overwrites the
   mmap_sem must be taken in write mode and all other anon_vma/i_mmap
   locks must be taken too.

2) It'd be a waste to add branches in the VM if nobody could possibly
   run KVM/GRU/XPMEM on the kernel, so mmu notifiers will only enabled
   if CONFIG_KVM=m/y. In the current kernel kvm won't yet take
   advantage of mmu notifiers, but this already allows to compile a
   KVM external module against a kernel with mmu notifiers enabled and
   from the next pull from kvm.git we'll start using them. And
   GRU/XPMEM will also be able to continue the development by enabling
   KVM=m in their config, until they submit all GRU/XPMEM GPLv2 code
   to the mainline kernel. Then they can also enable MMU_NOTIFIERS in
   the same way KVM does it (even if KVM=n). This guarantees nobody
   selects MMU_NOTIFIER=y if KVM and GRU and XPMEM are all =n.

The mmu_notifier_register call can fail because mm_take_all_locks may
be interrupted by a signal and return -EINTR. Because
mmu_notifier_reigster is used when a driver startup, a failure can be
gracefully handled. Here an example of the change applied to kvm to
register the mmu notifiers. Usually when a driver startups other
allocations are required anyway and -ENOMEM failure paths exists
already.

 struct  kvm *kvm_arch_create_vm(void)
 {
        struct kvm *kvm = kzalloc(sizeof(struct kvm), GFP_KERNEL);
+       int err;

        if (!kvm)
                return ERR_PTR(-ENOMEM);

        INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);

+       kvm->arch.mmu_notifier.ops = &kvm_mmu_notifier_ops;
+       err = mmu_notifier_register(&kvm->arch.mmu_notifier, current->mm);
+       if (err) {
+               kfree(kvm);
+               return ERR_PTR(err);
+       }
+
        return kvm;
 }

mmu_notifier_unregister returns void and it's reliable.

The patch also adds a few needed but missing includes that would prevent kernel
to compile after these changes on non-x86 archs (x86 didn't need them by luck).

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---

diff -r 082f312bc682 -r 9cf86778092b arch/x86/kvm/Kconfig
--- a/arch/x86/kvm/Kconfig	Thu Jun 05 17:30:17 2008 +0200
+++ b/arch/x86/kvm/Kconfig	Thu Jun 05 17:31:21 2008 +0200
@@ -21,6 +21,7 @@ config KVM
 	tristate "Kernel-based Virtual Machine (KVM) support"
 	depends on HAVE_KVM
 	select PREEMPT_NOTIFIERS
+	select MMU_NOTIFIER
 	select ANON_INODES
 	---help---
 	  Support hosting fully virtualized guest machines using hardware
diff -r 082f312bc682 -r 9cf86778092b include/linux/mm_types.h
--- a/include/linux/mm_types.h	Thu Jun 05 17:30:17 2008 +0200
+++ b/include/linux/mm_types.h	Thu Jun 05 17:31:21 2008 +0200
@@ -10,6 +10,7 @@
 #include <linux/rbtree.h>
 #include <linux/rwsem.h>
 #include <linux/completion.h>
+#include <linux/cpumask.h>
 #include <asm/page.h>
 #include <asm/mmu.h>
 
@@ -244,6 +245,9 @@ struct mm_struct {
 	struct file *exe_file;
 	unsigned long num_exe_file_vmas;
 #endif
+#ifdef CONFIG_MMU_NOTIFIER
+	struct mmu_notifier_mm *mmu_notifier_mm;
+#endif
 };
 
 #endif /* _LINUX_MM_TYPES_H */
diff -r 082f312bc682 -r 9cf86778092b include/linux/mmu_notifier.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/include/linux/mmu_notifier.h	Thu Jun 05 17:31:21 2008 +0200
@@ -0,0 +1,279 @@
+#ifndef _LINUX_MMU_NOTIFIER_H
+#define _LINUX_MMU_NOTIFIER_H
+
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/mm_types.h>
+
+struct mmu_notifier;
+struct mmu_notifier_ops;
+
+#ifdef CONFIG_MMU_NOTIFIER
+
+/*
+ * The mmu notifier_mm structure is allocated and installed in
+ * mm->mmu_notifier_mm inside the mm_take_all_locks() protected
+ * critical section and it's released only when mm_count reaches zero
+ * in mmdrop().
+ */
+struct mmu_notifier_mm {
+	/* all mmu notifiers registerd in this mm are queued in this list */
+	struct hlist_head list;
+	/* to serialize the list modifications and hlist_unhashed */
+	spinlock_t lock;
+};
+
+struct mmu_notifier_ops {
+	/*
+	 * Called either by mmu_notifier_unregister or when the mm is
+	 * being destroyed by exit_mmap, always before all pages are
+	 * freed. This can run concurrently with other mmu notifier
+	 * methods (the ones invoked outside the mm context) and it
+	 * should tear down all secondary mmu mappings and freeze the
+	 * secondary mmu. If this method isn't implemented you've to
+	 * be sure that nothing could possibly write to the pages
+	 * through the secondary mmu by the time the last thread with
+	 * tsk->mm == mm exits.
+	 *
+	 * As side note: the pages freed after ->release returns could
+	 * be immediately reallocated by the gart at an alias physical
+	 * address with a different cache model, so if ->release isn't
+	 * implemented because all _software_ driven memory accesses
+	 * through the secondary mmu are terminated by the time the
+	 * last thread of this mm quits, you've also to be sure that
+	 * speculative _hardware_ operations can't allocate dirty
+	 * cachelines in the cpu that could not be snooped and made
+	 * coherent with the other read and write operations happening
+	 * through the gart alias address, so leading to memory
+	 * corruption.
+	 */
+	void (*release)(struct mmu_notifier *mn,
+			struct mm_struct *mm);
+
+	/*
+	 * clear_flush_young is called after the VM is
+	 * test-and-clearing the young/accessed bitflag in the
+	 * pte. This way the VM will provide proper aging to the
+	 * accesses to the page through the secondary MMUs and not
+	 * only to the ones through the Linux pte.
+	 */
+	int (*clear_flush_young)(struct mmu_notifier *mn,
+				 struct mm_struct *mm,
+				 unsigned long address);
+
+	/*
+	 * Before this is invoked any secondary MMU is still ok to
+	 * read/write to the page previously pointed to by the Linux
+	 * pte because the page hasn't been freed yet and it won't be
+	 * freed until this returns. If required set_page_dirty has to
+	 * be called internally to this method.
+	 */
+	void (*invalidate_page)(struct mmu_notifier *mn,
+				struct mm_struct *mm,
+				unsigned long address);
+
+	/*
+	 * invalidate_range_start() and invalidate_range_end() must be
+	 * paired and are called only when the mmap_sem and/or the
+	 * locks protecting the reverse maps are held. The subsystem
+	 * must guarantee that no additional references are taken to
+	 * the pages in the range established between the call to
+	 * invalidate_range_start() and the matching call to
+	 * invalidate_range_end().
+	 *
+	 * Invalidation of multiple concurrent ranges may be
+	 * optionally permitted by the driver. Either way the
+	 * establishment of sptes is forbidden in the range passed to
+	 * invalidate_range_begin/end for the whole duration of the
+	 * invalidate_range_begin/end critical section.
+	 *
+	 * invalidate_range_start() is called when all pages in the
+	 * range are still mapped and have at least a refcount of one.
+	 *
+	 * invalidate_range_end() is called when all pages in the
+	 * range have been unmapped and the pages have been freed by
+	 * the VM.
+	 *
+	 * The VM will remove the page table entries and potentially
+	 * the page between invalidate_range_start() and
+	 * invalidate_range_end(). If the page must not be freed
+	 * because of pending I/O or other circumstances then the
+	 * invalidate_range_start() callback (or the initial mapping
+	 * by the driver) must make sure that the refcount is kept
+	 * elevated.
+	 *
+	 * If the driver increases the refcount when the pages are
+	 * initially mapped into an address space then either
+	 * invalidate_range_start() or invalidate_range_end() may
+	 * decrease the refcount. If the refcount is decreased on
+	 * invalidate_range_start() then the VM can free pages as page
+	 * table entries are removed.  If the refcount is only
+	 * droppped on invalidate_range_end() then the driver itself
+	 * will drop the last refcount but it must take care to flush
+	 * any secondary tlb before doing the final free on the
+	 * page. Pages will no longer be referenced by the linux
+	 * address space but may still be referenced by sptes until
+	 * the last refcount is dropped.
+	 */
+	void (*invalidate_range_start)(struct mmu_notifier *mn,
+				       struct mm_struct *mm,
+				       unsigned long start, unsigned long end);
+	void (*invalidate_range_end)(struct mmu_notifier *mn,
+				     struct mm_struct *mm,
+				     unsigned long start, unsigned long end);
+};
+
+/*
+ * The notifier chains are protected by mmap_sem and/or the reverse map
+ * semaphores. Notifier chains are only changed when all reverse maps and
+ * the mmap_sem locks are taken.
+ *
+ * Therefore notifier chains can only be traversed when either
+ *
+ * 1. mmap_sem is held.
+ * 2. One of the reverse map locks is held (i_mmap_lock or anon_vma->lock).
+ * 3. No other concurrent thread can access the list (release)
+ */
+struct mmu_notifier {
+	struct hlist_node hlist;
+	const struct mmu_notifier_ops *ops;
+};
+
+static inline int mm_has_notifiers(struct mm_struct *mm)
+{
+	return unlikely(mm->mmu_notifier_mm);
+}
+
+extern int mmu_notifier_register(struct mmu_notifier *mn,
+				 struct mm_struct *mm);
+extern int __mmu_notifier_register(struct mmu_notifier *mn,
+				   struct mm_struct *mm);
+extern void mmu_notifier_unregister(struct mmu_notifier *mn,
+				    struct mm_struct *mm);
+extern void __mmu_notifier_mm_destroy(struct mm_struct *mm);
+extern void __mmu_notifier_release(struct mm_struct *mm);
+extern int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					  unsigned long address);
+extern void __mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address);
+extern void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end);
+extern void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end);
+
+static inline void mmu_notifier_release(struct mm_struct *mm)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_release(mm);
+}
+
+static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					  unsigned long address)
+{
+	if (mm_has_notifiers(mm))
+		return __mmu_notifier_clear_flush_young(mm, address);
+	return 0;
+}
+
+static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_invalidate_page(mm, address);
+}
+
+static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_invalidate_range_start(mm, start, end);
+}
+
+static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_invalidate_range_end(mm, start, end);
+}
+
+static inline void mmu_notifier_mm_init(struct mm_struct *mm)
+{
+	mm->mmu_notifier_mm = NULL;
+}
+
+static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_mm_destroy(mm);
+}
+
+/*
+ * These two macros will sometime replace ptep_clear_flush.
+ * ptep_clear_flush is impleemnted as macro itself, so this also is
+ * implemented as a macro until ptep_clear_flush will converted to an
+ * inline function, to diminish the risk of compilation failure. The
+ * invalidate_page method over time can be moved outside the PT lock
+ * and these two macros can be later removed.
+ */
+#define ptep_clear_flush_notify(__vma, __address, __ptep)		\
+({									\
+	pte_t __pte;							\
+	struct vm_area_struct *___vma = __vma;				\
+	unsigned long ___address = __address;				\
+	__pte = ptep_clear_flush(___vma, ___address, __ptep);		\
+	mmu_notifier_invalidate_page(___vma->vm_mm, ___address);	\
+	__pte;								\
+})
+
+#define ptep_clear_flush_young_notify(__vma, __address, __ptep)		\
+({									\
+	int __young;							\
+	struct vm_area_struct *___vma = __vma;				\
+	unsigned long ___address = __address;				\
+	__young = ptep_clear_flush_young(___vma, ___address, __ptep);	\
+	__young |= mmu_notifier_clear_flush_young(___vma->vm_mm,	\
+						  ___address);		\
+	__young;							\
+})
+
+#else /* CONFIG_MMU_NOTIFIER */
+
+static inline void mmu_notifier_release(struct mm_struct *mm)
+{
+}
+
+static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					  unsigned long address)
+{
+	return 0;
+}
+
+static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address)
+{
+}
+
+static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+}
+
+static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+}
+
+static inline void mmu_notifier_mm_init(struct mm_struct *mm)
+{
+}
+
+static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
+{
+}
+
+#define ptep_clear_flush_young_notify ptep_clear_flush_young
+#define ptep_clear_flush_notify ptep_clear_flush
+
+#endif /* CONFIG_MMU_NOTIFIER */
+
+#endif /* _LINUX_MMU_NOTIFIER_H */
diff -r 082f312bc682 -r 9cf86778092b kernel/fork.c
--- a/kernel/fork.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/kernel/fork.c	Thu Jun 05 17:31:21 2008 +0200
@@ -54,6 +54,7 @@
 #include <linux/tty.h>
 #include <linux/proc_fs.h>
 #include <linux/blkdev.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -386,6 +387,7 @@ static struct mm_struct * mm_init(struct
 
 	if (likely(!mm_alloc_pgd(mm))) {
 		mm->def_flags = 0;
+		mmu_notifier_mm_init(mm);
 		return mm;
 	}
 
@@ -418,6 +420,7 @@ void __mmdrop(struct mm_struct *mm)
 	BUG_ON(mm == &init_mm);
 	mm_free_pgd(mm);
 	destroy_context(mm);
+	mmu_notifier_mm_destroy(mm);
 	free_mm(mm);
 }
 EXPORT_SYMBOL_GPL(__mmdrop);
diff -r 082f312bc682 -r 9cf86778092b mm/Kconfig
--- a/mm/Kconfig	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/Kconfig	Thu Jun 05 17:31:21 2008 +0200
@@ -205,3 +205,6 @@ config VIRT_TO_BUS
 config VIRT_TO_BUS
 	def_bool y
 	depends on !ARCH_NO_VIRT_TO_BUS
+
+config MMU_NOTIFIER
+	bool
diff -r 082f312bc682 -r 9cf86778092b mm/Makefile
--- a/mm/Makefile	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/Makefile	Thu Jun 05 17:31:21 2008 +0200
@@ -33,4 +33,5 @@ obj-$(CONFIG_SMP) += allocpercpu.o
 obj-$(CONFIG_SMP) += allocpercpu.o
 obj-$(CONFIG_QUICKLIST) += quicklist.o
 obj-$(CONFIG_CGROUP_MEM_RES_CTLR) += memcontrol.o
+obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
 
diff -r 082f312bc682 -r 9cf86778092b mm/filemap_xip.c
--- a/mm/filemap_xip.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/filemap_xip.c	Thu Jun 05 17:31:21 2008 +0200
@@ -188,7 +188,7 @@ __xip_unmap (struct address_space * mapp
 		if (pte) {
 			/* Nuke the page table entry. */
 			flush_cache_page(vma, address, pte_pfn(*pte));
-			pteval = ptep_clear_flush(vma, address, pte);
+			pteval = ptep_clear_flush_notify(vma, address, pte);
 			page_remove_rmap(page, vma);
 			dec_mm_counter(mm, file_rss);
 			BUG_ON(pte_dirty(pteval));
diff -r 082f312bc682 -r 9cf86778092b mm/fremap.c
--- a/mm/fremap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/fremap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -15,6 +15,7 @@
 #include <linux/rmap.h>
 #include <linux/module.h>
 #include <linux/syscalls.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/mmu_context.h>
 #include <asm/cacheflush.h>
@@ -214,7 +215,9 @@ asmlinkage long sys_remap_file_pages(uns
 		spin_unlock(&mapping->i_mmap_lock);
 	}
 
+	mmu_notifier_invalidate_range_start(mm, start, start + size);
 	err = populate_range(mm, vma, start, size, pgoff);
+	mmu_notifier_invalidate_range_end(mm, start, start + size);
 	if (!err && !(flags & MAP_NONBLOCK)) {
 		if (unlikely(has_write_lock)) {
 			downgrade_write(&mm->mmap_sem);
diff -r 082f312bc682 -r 9cf86778092b mm/hugetlb.c
--- a/mm/hugetlb.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/hugetlb.c	Thu Jun 05 17:31:21 2008 +0200
@@ -14,6 +14,7 @@
 #include <linux/mempolicy.h>
 #include <linux/cpuset.h>
 #include <linux/mutex.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/page.h>
 #include <asm/pgtable.h>
@@ -823,6 +824,7 @@ void __unmap_hugepage_range(struct vm_ar
 	BUG_ON(start & ~HPAGE_MASK);
 	BUG_ON(end & ~HPAGE_MASK);
 
+	mmu_notifier_invalidate_range_start(mm, start, end);
 	spin_lock(&mm->page_table_lock);
 	for (address = start; address < end; address += HPAGE_SIZE) {
 		ptep = huge_pte_offset(mm, address);
@@ -843,6 +845,7 @@ void __unmap_hugepage_range(struct vm_ar
 	}
 	spin_unlock(&mm->page_table_lock);
 	flush_tlb_range(vma, start, end);
+	mmu_notifier_invalidate_range_end(mm, start, end);
 	list_for_each_entry_safe(page, tmp, &page_list, lru) {
 		list_del(&page->lru);
 		put_page(page);
diff -r 082f312bc682 -r 9cf86778092b mm/memory.c
--- a/mm/memory.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/memory.c	Thu Jun 05 17:31:21 2008 +0200
@@ -51,6 +51,7 @@
 #include <linux/init.h>
 #include <linux/writeback.h>
 #include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/pgalloc.h>
 #include <asm/uaccess.h>
@@ -649,6 +650,7 @@ int copy_page_range(struct mm_struct *ds
 	unsigned long next;
 	unsigned long addr = vma->vm_start;
 	unsigned long end = vma->vm_end;
+	int ret;
 
 	/*
 	 * Don't copy ptes where a page fault will fill them correctly.
@@ -664,17 +666,33 @@ int copy_page_range(struct mm_struct *ds
 	if (is_vm_hugetlb_page(vma))
 		return copy_hugetlb_page_range(dst_mm, src_mm, vma);
 
+	/*
+	 * We need to invalidate the secondary MMU mappings only when
+	 * there could be a permission downgrade on the ptes of the
+	 * parent mm. And a permission downgrade will only happen if
+	 * is_cow_mapping() returns true.
+	 */
+	if (is_cow_mapping(vma->vm_flags))
+		mmu_notifier_invalidate_range_start(src_mm, addr, end);
+
+	ret = 0;
 	dst_pgd = pgd_offset(dst_mm, addr);
 	src_pgd = pgd_offset(src_mm, addr);
 	do {
 		next = pgd_addr_end(addr, end);
 		if (pgd_none_or_clear_bad(src_pgd))
 			continue;
-		if (copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
-						vma, addr, next))
-			return -ENOMEM;
+		if (unlikely(copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
+					    vma, addr, next))) {
+			ret = -ENOMEM;
+			break;
+		}
 	} while (dst_pgd++, src_pgd++, addr = next, addr != end);
-	return 0;
+
+	if (is_cow_mapping(vma->vm_flags))
+		mmu_notifier_invalidate_range_end(src_mm,
+						  vma->vm_start, end);
+	return ret;
 }
 
 static unsigned long zap_pte_range(struct mmu_gather *tlb,
@@ -878,7 +896,9 @@ unsigned long unmap_vmas(struct mmu_gath
 	unsigned long start = start_addr;
 	spinlock_t *i_mmap_lock = details? details->i_mmap_lock: NULL;
 	int fullmm = (*tlbp)->fullmm;
+	struct mm_struct *mm = vma->vm_mm;
 
+	mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
 	for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next) {
 		unsigned long end;
 
@@ -929,6 +949,7 @@ unsigned long unmap_vmas(struct mmu_gath
 		}
 	}
 out:
+	mmu_notifier_invalidate_range_end(mm, start_addr, end_addr);
 	return start;	/* which is now the end (or restart) address */
 }
 
@@ -1561,10 +1582,11 @@ int apply_to_page_range(struct mm_struct
 {
 	pgd_t *pgd;
 	unsigned long next;
-	unsigned long end = addr + size;
+	unsigned long start = addr, end = addr + size;
 	int err;
 
 	BUG_ON(addr >= end);
+	mmu_notifier_invalidate_range_start(mm, start, end);
 	pgd = pgd_offset(mm, addr);
 	do {
 		next = pgd_addr_end(addr, end);
@@ -1572,6 +1594,7 @@ int apply_to_page_range(struct mm_struct
 		if (err)
 			break;
 	} while (pgd++, addr = next, addr != end);
+	mmu_notifier_invalidate_range_end(mm, start, end);
 	return err;
 }
 EXPORT_SYMBOL_GPL(apply_to_page_range);
@@ -1773,7 +1796,7 @@ gotten:
 		 * seen in the presence of one thread doing SMC and another
 		 * thread doing COW.
 		 */
-		ptep_clear_flush(vma, address, page_table);
+		ptep_clear_flush_notify(vma, address, page_table);
 		set_pte_at(mm, address, page_table, entry);
 		update_mmu_cache(vma, address, entry);
 		lru_cache_add_active(new_page);
diff -r 082f312bc682 -r 9cf86778092b mm/mmap.c
--- a/mm/mmap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mmap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -26,6 +26,7 @@
 #include <linux/mount.h>
 #include <linux/mempolicy.h>
 #include <linux/rmap.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
@@ -2048,6 +2049,7 @@ void exit_mmap(struct mm_struct *mm)
 
 	/* mm's last user has gone, and its about to be pulled down */
 	arch_exit_mmap(mm);
+	mmu_notifier_release(mm);
 
 	lru_add_drain();
 	flush_cache_mm(mm);
diff -r 082f312bc682 -r 9cf86778092b mm/mmu_notifier.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mm/mmu_notifier.c	Thu Jun 05 17:31:21 2008 +0200
@@ -0,0 +1,276 @@
+/*
+ *  linux/mm/mmu_notifier.c
+ *
+ *  Copyright (C) 2008  Qumranet, Inc.
+ *  Copyright (C) 2008  SGI
+ *             Christoph Lameter <clameter@sgi.com>
+ *
+ *  This work is licensed under the terms of the GNU GPL, version 2. See
+ *  the COPYING file in the top-level directory.
+ */
+
+#include <linux/mmu_notifier.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/err.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+
+/*
+ * This function can't run concurrently against mmu_notifier_register
+ * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
+ * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
+ * in parallel despite there being no task using this mm any more,
+ * through the vmas outside of the exit_mmap context, such as with
+ * vmtruncate. This serializes against mmu_notifier_unregister with
+ * the mmu_notifier_mm->lock in addition to RCU and it serializes
+ * against the other mmu notifiers with RCU. struct mmu_notifier_mm
+ * can't go away from under us as exit_mmap holds an mm_count pin
+ * itself.
+ */
+void __mmu_notifier_release(struct mm_struct *mm)
+{
+	struct mmu_notifier *mn;
+
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
+		mn = hlist_entry(mm->mmu_notifier_mm->list.first,
+				 struct mmu_notifier,
+				 hlist);
+		/*
+		 * We arrived before mmu_notifier_unregister so
+		 * mmu_notifier_unregister will do nothing other than
+		 * to wait ->release to finish and
+		 * mmu_notifier_unregister to return.
+		 */
+		hlist_del_init_rcu(&mn->hlist);
+		/*
+		 * RCU here will block mmu_notifier_unregister until
+		 * ->release returns.
+		 */
+		rcu_read_lock();
+		spin_unlock(&mm->mmu_notifier_mm->lock);
+		/*
+		 * if ->release runs before mmu_notifier_unregister it
+		 * must be handled as it's the only way for the driver
+		 * to flush all existing sptes and stop the driver
+		 * from establishing any more sptes before all the
+		 * pages in the mm are freed.
+		 */
+		if (mn->ops->release)
+			mn->ops->release(mn, mm);
+		rcu_read_unlock();
+		spin_lock(&mm->mmu_notifier_mm->lock);
+	}
+	spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	/*
+	 * synchronize_rcu here prevents mmu_notifier_release to
+	 * return to exit_mmap (which would proceed freeing all pages
+	 * in the mm) until the ->release method returns, if it was
+	 * invoked by mmu_notifier_unregister.
+	 *
+	 * The mmu_notifier_mm can't go away from under us because one
+	 * mm_count is hold by exit_mmap.
+	 */
+	synchronize_rcu();
+}
+
+/*
+ * If no young bitflag is supported by the hardware, ->clear_flush_young can
+ * unmap the address and return 1 or 0 depending if the mapping previously
+ * existed or not.
+ */
+int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					unsigned long address)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+	int young = 0;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->clear_flush_young)
+			young |= mn->ops->clear_flush_young(mn, mm, address);
+	}
+	rcu_read_unlock();
+
+	return young;
+}
+
+void __mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->invalidate_page)
+			mn->ops->invalidate_page(mn, mm, address);
+	}
+	rcu_read_unlock();
+}
+
+void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->invalidate_range_start)
+			mn->ops->invalidate_range_start(mn, mm, start, end);
+	}
+	rcu_read_unlock();
+}
+
+void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->invalidate_range_end)
+			mn->ops->invalidate_range_end(mn, mm, start, end);
+	}
+	rcu_read_unlock();
+}
+
+static int do_mmu_notifier_register(struct mmu_notifier *mn,
+				    struct mm_struct *mm,
+				    int take_mmap_sem)
+{
+	struct mmu_notifier_mm * mmu_notifier_mm;
+	int ret;
+
+	BUG_ON(atomic_read(&mm->mm_users) <= 0);
+
+	ret = -ENOMEM;
+	mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
+	if (unlikely(!mmu_notifier_mm))
+		goto out;
+
+	if (take_mmap_sem)
+		down_write(&mm->mmap_sem);
+	ret = mm_take_all_locks(mm);
+	if (unlikely(ret))
+		goto out_cleanup;
+
+	if (!mm_has_notifiers(mm)) {
+		INIT_HLIST_HEAD(&mmu_notifier_mm->list);
+		spin_lock_init(&mmu_notifier_mm->lock);
+		mm->mmu_notifier_mm = mmu_notifier_mm;
+		mmu_notifier_mm = NULL;
+	}
+	atomic_inc(&mm->mm_count);
+
+	/*
+	 * Serialize the update against mmu_notifier_unregister. A
+	 * side note: mmu_notifier_release can't run concurrently with
+	 * us because we hold the mm_users pin (either implicitly as
+	 * current->mm or explicitly with get_task_mm() or similar).
+	 * We can't race against any other mmu notifier method either
+	 * thanks to mm_take_all_locks().
+	 */
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
+	spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	mm_drop_all_locks(mm);
+out_cleanup:
+	if (take_mmap_sem)
+		up_write(&mm->mmap_sem);
+	/* kfree() does nothing if mmu_notifier_mm is NULL */
+	kfree(mmu_notifier_mm);
+out:
+	BUG_ON(atomic_read(&mm->mm_users) <= 0);
+	return ret;
+}
+
+/*
+ * Must not hold mmap_sem nor any other VM related lock when calling
+ * this registration function. Must also ensure mm_users can't go down
+ * to zero while this runs to avoid races with mmu_notifier_release,
+ * so mm has to be current->mm or the mm should be pinned safely such
+ * as with get_task_mm(). If the mm is not current->mm, the mm_users
+ * pin should be released by calling mmput after mmu_notifier_register
+ * returns. mmu_notifier_unregister must be always called to
+ * unregister the notifier. mm_count is automatically pinned to allow
+ * mmu_notifier_unregister to safely run at any time later, before or
+ * after exit_mmap. ->release will always be called before exit_mmap
+ * frees the pages.
+ */
+int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	return do_mmu_notifier_register(mn, mm, 1);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_register);
+
+/*
+ * Same as mmu_notifier_register but here the caller must hold the
+ * mmap_sem in write mode.
+ */
+int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	return do_mmu_notifier_register(mn, mm, 0);
+}
+EXPORT_SYMBOL_GPL(__mmu_notifier_register);
+
+/* this is called after the last mmu_notifier_unregister() returned */
+void __mmu_notifier_mm_destroy(struct mm_struct *mm)
+{
+	BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
+	kfree(mm->mmu_notifier_mm);
+	mm->mmu_notifier_mm = LIST_POISON1; /* debug */
+}
+
+/*
+ * This releases the mm_count pin automatically and frees the mm
+ * structure if it was the last user of it. It serializes against
+ * running mmu notifiers with RCU and against mmu_notifier_unregister
+ * with the unregister lock + RCU. All sptes must be dropped before
+ * calling mmu_notifier_unregister. ->release or any other notifier
+ * method may be invoked concurrently with mmu_notifier_unregister,
+ * and only after mmu_notifier_unregister returned we're guaranteed
+ * that ->release or any other method can't run anymore.
+ */
+void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	BUG_ON(atomic_read(&mm->mm_count) <= 0);
+
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	if (!hlist_unhashed(&mn->hlist)) {
+		hlist_del_rcu(&mn->hlist);
+
+		/*
+		 * RCU here will force exit_mmap to wait ->release to finish
+		 * before freeing the pages.
+		 */
+		rcu_read_lock();
+		spin_unlock(&mm->mmu_notifier_mm->lock);
+		/*
+		 * exit_mmap will block in mmu_notifier_release to
+		 * guarantee ->release is called before freeing the
+		 * pages.
+		 */
+		if (mn->ops->release)
+			mn->ops->release(mn, mm);
+		rcu_read_unlock();
+	} else
+		spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	/*
+	 * Wait any running method to finish, of course including
+	 * ->release if it was run by mmu_notifier_relase instead of us.
+	 */
+	synchronize_rcu();
+
+	BUG_ON(atomic_read(&mm->mm_count) <= 0);
+
+	mmdrop(mm);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
diff -r 082f312bc682 -r 9cf86778092b mm/mprotect.c
--- a/mm/mprotect.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mprotect.c	Thu Jun 05 17:31:21 2008 +0200
@@ -21,6 +21,7 @@
 #include <linux/syscalls.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
+#include <linux/mmu_notifier.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
 #include <asm/cacheflush.h>
@@ -207,10 +208,12 @@ success:
 		dirty_accountable = 1;
 	}
 
+	mmu_notifier_invalidate_range_start(mm, start, end);
 	if (is_vm_hugetlb_page(vma))
 		hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 	else
 		change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
+	mmu_notifier_invalidate_range_end(mm, start, end);
 	vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 	vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 	return 0;
diff -r 082f312bc682 -r 9cf86778092b mm/mremap.c
--- a/mm/mremap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mremap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -18,6 +18,7 @@
 #include <linux/highmem.h>
 #include <linux/security.h>
 #include <linux/syscalls.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
@@ -74,7 +75,11 @@ static void move_ptes(struct vm_area_str
 	struct mm_struct *mm = vma->vm_mm;
 	pte_t *old_pte, *new_pte, pte;
 	spinlock_t *old_ptl, *new_ptl;
+	unsigned long old_start;
 
+	old_start = old_addr;
+	mmu_notifier_invalidate_range_start(vma->vm_mm,
+					    old_start, old_end);
 	if (vma->vm_file) {
 		/*
 		 * Subtle point from Rajesh Venkatasubramanian: before
@@ -116,6 +121,7 @@ static void move_ptes(struct vm_area_str
 	pte_unmap_unlock(old_pte - 1, old_ptl);
 	if (mapping)
 		spin_unlock(&mapping->i_mmap_lock);
+	mmu_notifier_invalidate_range_end(vma->vm_mm, old_start, old_end);
 }
 
 #define LATENCY_LIMIT	(64 * PAGE_SIZE)
diff -r 082f312bc682 -r 9cf86778092b mm/rmap.c
--- a/mm/rmap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/rmap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -49,6 +49,7 @@
 #include <linux/module.h>
 #include <linux/kallsyms.h>
 #include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/tlbflush.h>
 
@@ -287,7 +288,7 @@ static int page_referenced_one(struct pa
 	if (vma->vm_flags & VM_LOCKED) {
 		referenced++;
 		*mapcount = 1;	/* break early from loop */
-	} else if (ptep_clear_flush_young(vma, address, pte))
+	} else if (ptep_clear_flush_young_notify(vma, address, pte))
 		referenced++;
 
 	/* Pretend the page is referenced if the task has the
@@ -457,7 +458,7 @@ static int page_mkclean_one(struct page 
 		pte_t entry;
 
 		flush_cache_page(vma, address, pte_pfn(*pte));
-		entry = ptep_clear_flush(vma, address, pte);
+		entry = ptep_clear_flush_notify(vma, address, pte);
 		entry = pte_wrprotect(entry);
 		entry = pte_mkclean(entry);
 		set_pte_at(mm, address, pte, entry);
@@ -717,14 +718,14 @@ static int try_to_unmap_one(struct page 
 	 * skipped over this mm) then we should reactivate it.
 	 */
 	if (!migration && ((vma->vm_flags & VM_LOCKED) ||
-			(ptep_clear_flush_young(vma, address, pte)))) {
+			(ptep_clear_flush_young_notify(vma, address, pte)))) {
 		ret = SWAP_FAIL;
 		goto out_unmap;
 	}
 
 	/* Nuke the page table entry. */
 	flush_cache_page(vma, address, page_to_pfn(page));
-	pteval = ptep_clear_flush(vma, address, pte);
+	pteval = ptep_clear_flush_notify(vma, address, pte);
 
 	/* Move the dirty bit to the physical page now the pte is gone. */
 	if (pte_dirty(pteval))
@@ -849,12 +850,12 @@ static void try_to_unmap_cluster(unsigne
 		page = vm_normal_page(vma, address, *pte);
 		BUG_ON(!page || PageAnon(page));
 
-		if (ptep_clear_flush_young(vma, address, pte))
+		if (ptep_clear_flush_young_notify(vma, address, pte))
 			continue;
 
 		/* Nuke the page table entry. */
 		flush_cache_page(vma, address, pte_pfn(*pte));
-		pteval = ptep_clear_flush(vma, address, pte);
+		pteval = ptep_clear_flush_notify(vma, address, pte);
 
 		/* If nonlinear, store the file page offset in the pte. */
 		if (page->index != linear_page_index(vma, address))

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[PATCH 3 of 3] mmu-notifier-core

[Andrea Arcangeli]

From: Andrea Arcangeli <andrea@qumranet.com>

With KVM/GFP/XPMEM there isn't just the primary CPU MMU pointing to
pages. There are secondary MMUs (with secondary sptes and secondary
tlbs) too. sptes in the kvm case are shadow pagetables, but when I say
spte in mmu-notifier context, I mean "secondary pte". In GRU case
there's no actual secondary pte and there's only a secondary tlb
because the GRU secondary MMU has no knowledge about sptes and every
secondary tlb miss event in the MMU always generates a page fault that
has to be resolved by the CPU (this is not the case of KVM where the a
secondary tlb miss will walk sptes in hardware and it will refill the
secondary tlb transparently to software if the corresponding spte is
present). The same way zap_page_range has to invalidate the pte before
freeing the page, the spte (and secondary tlb) must also be
invalidated before any page is freed and reused.

Currently we take a page_count pin on every page mapped by sptes, but
that means the pages can't be swapped whenever they're mapped by any
spte because they're part of the guest working set. Furthermore a spte
unmap event can immediately lead to a page to be freed when the pin is
released (so requiring the same complex and relatively slow tlb_gather
smp safe logic we have in zap_page_range and that can be avoided
completely if the spte unmap event doesn't require an unpin of the
page previously mapped in the secondary MMU).

The mmu notifiers allow kvm/GRU/XPMEM to attach to the tsk->mm and
know when the VM is swapping or freeing or doing anything on the
primary MMU so that the secondary MMU code can drop sptes before the
pages are freed, avoiding all page pinning and allowing 100% reliable
swapping of guest physical address space. Furthermore it avoids the
code that teardown the mappings of the secondary MMU, to implement a
logic like tlb_gather in zap_page_range that would require many IPI to
flush other cpu tlbs, for each fixed number of spte unmapped.

To make an example: if what happens on the primary MMU is a protection
downgrade (from writeable to wrprotect) the secondary MMU mappings
will be invalidated, and the next secondary-mmu-page-fault will call
get_user_pages and trigger a do_wp_page through get_user_pages if it
called get_user_pages with write=1, and it'll re-establishing an
updated spte or secondary-tlb-mapping on the copied page. Or it will
setup a readonly spte or readonly tlb mapping if it's a guest-read, if
it calls get_user_pages with write=0. This is just an example.

This allows to map any page pointed by any pte (and in turn visible in
the primary CPU MMU), into a secondary MMU (be it a pure tlb like GRU,
or an full MMU with both sptes and secondary-tlb like the
shadow-pagetable layer with kvm), or a remote DMA in software like
XPMEM (hence needing of schedule in XPMEM code to send the invalidate
to the remote node, while no need to schedule in kvm/gru as it's an
immediate event like invalidating primary-mmu pte).

At least for KVM without this patch it's impossible to swap guests
reliably. And having this feature and removing the page pin allows
several other optimizations that simplify life considerably.

Dependencies:

1) mm_take_all_locks() to register the mmu notifier when the whole VM
   isn't doing anything with "mm". This allows mmu notifier users to
   keep track if the VM is in the middle of the
   invalidate_range_begin/end critical section with an atomic counter
   incraese in range_begin and decreased in range_end. No secondary
   MMU page fault is allowed to map any spte or secondary tlb
   reference, while the VM is in the middle of range_begin/end as any
   page returned by get_user_pages in that critical section could
   later immediately be freed without any further ->invalidate_page
   notification (invalidate_range_begin/end works on ranges and
   ->invalidate_page isn't called immediately before freeing the
   page). To stop all page freeing and pagetable overwrites the
   mmap_sem must be taken in write mode and all other anon_vma/i_mmap
   locks must be taken too.

2) It'd be a waste to add branches in the VM if nobody could possibly
   run KVM/GRU/XPMEM on the kernel, so mmu notifiers will only enabled
   if CONFIG_KVM=m/y. In the current kernel kvm won't yet take
   advantage of mmu notifiers, but this already allows to compile a
   KVM external module against a kernel with mmu notifiers enabled and
   from the next pull from kvm.git we'll start using them. And
   GRU/XPMEM will also be able to continue the development by enabling
   KVM=m in their config, until they submit all GRU/XPMEM GPLv2 code
   to the mainline kernel. Then they can also enable MMU_NOTIFIERS in
   the same way KVM does it (even if KVM=n). This guarantees nobody
   selects MMU_NOTIFIER=y if KVM and GRU and XPMEM are all =n.

The mmu_notifier_register call can fail because mm_take_all_locks may
be interrupted by a signal and return -EINTR. Because
mmu_notifier_reigster is used when a driver startup, a failure can be
gracefully handled. Here an example of the change applied to kvm to
register the mmu notifiers. Usually when a driver startups other
allocations are required anyway and -ENOMEM failure paths exists
already.

 struct  kvm *kvm_arch_create_vm(void)
 {
        struct kvm *kvm = kzalloc(sizeof(struct kvm), GFP_KERNEL);
+       int err;

        if (!kvm)
                return ERR_PTR(-ENOMEM);

        INIT_LIST_HEAD(&kvm->arch.active_mmu_pages);

+       kvm->arch.mmu_notifier.ops = &kvm_mmu_notifier_ops;
+       err = mmu_notifier_register(&kvm->arch.mmu_notifier, current->mm);
+       if (err) {
+               kfree(kvm);
+               return ERR_PTR(err);
+       }
+
        return kvm;
 }

mmu_notifier_unregister returns void and it's reliable.

The patch also adds a few needed but missing includes that would prevent kernel
to compile after these changes on non-x86 archs (x86 didn't need them by luck).

Signed-off-by: Andrea Arcangeli <andrea@qumranet.com>
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
---

diff -r 082f312bc682 -r 9cf86778092b arch/x86/kvm/Kconfig
--- a/arch/x86/kvm/Kconfig	Thu Jun 05 17:30:17 2008 +0200
+++ b/arch/x86/kvm/Kconfig	Thu Jun 05 17:31:21 2008 +0200
@@ -21,6 +21,7 @@ config KVM
 	tristate "Kernel-based Virtual Machine (KVM) support"
 	depends on HAVE_KVM
 	select PREEMPT_NOTIFIERS
+	select MMU_NOTIFIER
 	select ANON_INODES
 	---help---
 	  Support hosting fully virtualized guest machines using hardware
diff -r 082f312bc682 -r 9cf86778092b include/linux/mm_types.h
--- a/include/linux/mm_types.h	Thu Jun 05 17:30:17 2008 +0200
+++ b/include/linux/mm_types.h	Thu Jun 05 17:31:21 2008 +0200
@@ -10,6 +10,7 @@
 #include <linux/rbtree.h>
 #include <linux/rwsem.h>
 #include <linux/completion.h>
+#include <linux/cpumask.h>
 #include <asm/page.h>
 #include <asm/mmu.h>
 
@@ -244,6 +245,9 @@ struct mm_struct {
 	struct file *exe_file;
 	unsigned long num_exe_file_vmas;
 #endif
+#ifdef CONFIG_MMU_NOTIFIER
+	struct mmu_notifier_mm *mmu_notifier_mm;
+#endif
 };
 
 #endif /* _LINUX_MM_TYPES_H */
diff -r 082f312bc682 -r 9cf86778092b include/linux/mmu_notifier.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/include/linux/mmu_notifier.h	Thu Jun 05 17:31:21 2008 +0200
@@ -0,0 +1,279 @@
+#ifndef _LINUX_MMU_NOTIFIER_H
+#define _LINUX_MMU_NOTIFIER_H
+
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/mm_types.h>
+
+struct mmu_notifier;
+struct mmu_notifier_ops;
+
+#ifdef CONFIG_MMU_NOTIFIER
+
+/*
+ * The mmu notifier_mm structure is allocated and installed in
+ * mm->mmu_notifier_mm inside the mm_take_all_locks() protected
+ * critical section and it's released only when mm_count reaches zero
+ * in mmdrop().
+ */
+struct mmu_notifier_mm {
+	/* all mmu notifiers registerd in this mm are queued in this list */
+	struct hlist_head list;
+	/* to serialize the list modifications and hlist_unhashed */
+	spinlock_t lock;
+};
+
+struct mmu_notifier_ops {
+	/*
+	 * Called either by mmu_notifier_unregister or when the mm is
+	 * being destroyed by exit_mmap, always before all pages are
+	 * freed. This can run concurrently with other mmu notifier
+	 * methods (the ones invoked outside the mm context) and it
+	 * should tear down all secondary mmu mappings and freeze the
+	 * secondary mmu. If this method isn't implemented you've to
+	 * be sure that nothing could possibly write to the pages
+	 * through the secondary mmu by the time the last thread with
+	 * tsk->mm == mm exits.
+	 *
+	 * As side note: the pages freed after ->release returns could
+	 * be immediately reallocated by the gart at an alias physical
+	 * address with a different cache model, so if ->release isn't
+	 * implemented because all _software_ driven memory accesses
+	 * through the secondary mmu are terminated by the time the
+	 * last thread of this mm quits, you've also to be sure that
+	 * speculative _hardware_ operations can't allocate dirty
+	 * cachelines in the cpu that could not be snooped and made
+	 * coherent with the other read and write operations happening
+	 * through the gart alias address, so leading to memory
+	 * corruption.
+	 */
+	void (*release)(struct mmu_notifier *mn,
+			struct mm_struct *mm);
+
+	/*
+	 * clear_flush_young is called after the VM is
+	 * test-and-clearing the young/accessed bitflag in the
+	 * pte. This way the VM will provide proper aging to the
+	 * accesses to the page through the secondary MMUs and not
+	 * only to the ones through the Linux pte.
+	 */
+	int (*clear_flush_young)(struct mmu_notifier *mn,
+				 struct mm_struct *mm,
+				 unsigned long address);
+
+	/*
+	 * Before this is invoked any secondary MMU is still ok to
+	 * read/write to the page previously pointed to by the Linux
+	 * pte because the page hasn't been freed yet and it won't be
+	 * freed until this returns. If required set_page_dirty has to
+	 * be called internally to this method.
+	 */
+	void (*invalidate_page)(struct mmu_notifier *mn,
+				struct mm_struct *mm,
+				unsigned long address);
+
+	/*
+	 * invalidate_range_start() and invalidate_range_end() must be
+	 * paired and are called only when the mmap_sem and/or the
+	 * locks protecting the reverse maps are held. The subsystem
+	 * must guarantee that no additional references are taken to
+	 * the pages in the range established between the call to
+	 * invalidate_range_start() and the matching call to
+	 * invalidate_range_end().
+	 *
+	 * Invalidation of multiple concurrent ranges may be
+	 * optionally permitted by the driver. Either way the
+	 * establishment of sptes is forbidden in the range passed to
+	 * invalidate_range_begin/end for the whole duration of the
+	 * invalidate_range_begin/end critical section.
+	 *
+	 * invalidate_range_start() is called when all pages in the
+	 * range are still mapped and have at least a refcount of one.
+	 *
+	 * invalidate_range_end() is called when all pages in the
+	 * range have been unmapped and the pages have been freed by
+	 * the VM.
+	 *
+	 * The VM will remove the page table entries and potentially
+	 * the page between invalidate_range_start() and
+	 * invalidate_range_end(). If the page must not be freed
+	 * because of pending I/O or other circumstances then the
+	 * invalidate_range_start() callback (or the initial mapping
+	 * by the driver) must make sure that the refcount is kept
+	 * elevated.
+	 *
+	 * If the driver increases the refcount when the pages are
+	 * initially mapped into an address space then either
+	 * invalidate_range_start() or invalidate_range_end() may
+	 * decrease the refcount. If the refcount is decreased on
+	 * invalidate_range_start() then the VM can free pages as page
+	 * table entries are removed.  If the refcount is only
+	 * droppped on invalidate_range_end() then the driver itself
+	 * will drop the last refcount but it must take care to flush
+	 * any secondary tlb before doing the final free on the
+	 * page. Pages will no longer be referenced by the linux
+	 * address space but may still be referenced by sptes until
+	 * the last refcount is dropped.
+	 */
+	void (*invalidate_range_start)(struct mmu_notifier *mn,
+				       struct mm_struct *mm,
+				       unsigned long start, unsigned long end);
+	void (*invalidate_range_end)(struct mmu_notifier *mn,
+				     struct mm_struct *mm,
+				     unsigned long start, unsigned long end);
+};
+
+/*
+ * The notifier chains are protected by mmap_sem and/or the reverse map
+ * semaphores. Notifier chains are only changed when all reverse maps and
+ * the mmap_sem locks are taken.
+ *
+ * Therefore notifier chains can only be traversed when either
+ *
+ * 1. mmap_sem is held.
+ * 2. One of the reverse map locks is held (i_mmap_lock or anon_vma->lock).
+ * 3. No other concurrent thread can access the list (release)
+ */
+struct mmu_notifier {
+	struct hlist_node hlist;
+	const struct mmu_notifier_ops *ops;
+};
+
+static inline int mm_has_notifiers(struct mm_struct *mm)
+{
+	return unlikely(mm->mmu_notifier_mm);
+}
+
+extern int mmu_notifier_register(struct mmu_notifier *mn,
+				 struct mm_struct *mm);
+extern int __mmu_notifier_register(struct mmu_notifier *mn,
+				   struct mm_struct *mm);
+extern void mmu_notifier_unregister(struct mmu_notifier *mn,
+				    struct mm_struct *mm);
+extern void __mmu_notifier_mm_destroy(struct mm_struct *mm);
+extern void __mmu_notifier_release(struct mm_struct *mm);
+extern int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					  unsigned long address);
+extern void __mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address);
+extern void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end);
+extern void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end);
+
+static inline void mmu_notifier_release(struct mm_struct *mm)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_release(mm);
+}
+
+static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					  unsigned long address)
+{
+	if (mm_has_notifiers(mm))
+		return __mmu_notifier_clear_flush_young(mm, address);
+	return 0;
+}
+
+static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_invalidate_page(mm, address);
+}
+
+static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_invalidate_range_start(mm, start, end);
+}
+
+static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_invalidate_range_end(mm, start, end);
+}
+
+static inline void mmu_notifier_mm_init(struct mm_struct *mm)
+{
+	mm->mmu_notifier_mm = NULL;
+}
+
+static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
+{
+	if (mm_has_notifiers(mm))
+		__mmu_notifier_mm_destroy(mm);
+}
+
+/*
+ * These two macros will sometime replace ptep_clear_flush.
+ * ptep_clear_flush is impleemnted as macro itself, so this also is
+ * implemented as a macro until ptep_clear_flush will converted to an
+ * inline function, to diminish the risk of compilation failure. The
+ * invalidate_page method over time can be moved outside the PT lock
+ * and these two macros can be later removed.
+ */
+#define ptep_clear_flush_notify(__vma, __address, __ptep)		\
+({									\
+	pte_t __pte;							\
+	struct vm_area_struct *___vma = __vma;				\
+	unsigned long ___address = __address;				\
+	__pte = ptep_clear_flush(___vma, ___address, __ptep);		\
+	mmu_notifier_invalidate_page(___vma->vm_mm, ___address);	\
+	__pte;								\
+})
+
+#define ptep_clear_flush_young_notify(__vma, __address, __ptep)		\
+({									\
+	int __young;							\
+	struct vm_area_struct *___vma = __vma;				\
+	unsigned long ___address = __address;				\
+	__young = ptep_clear_flush_young(___vma, ___address, __ptep);	\
+	__young |= mmu_notifier_clear_flush_young(___vma->vm_mm,	\
+						  ___address);		\
+	__young;							\
+})
+
+#else /* CONFIG_MMU_NOTIFIER */
+
+static inline void mmu_notifier_release(struct mm_struct *mm)
+{
+}
+
+static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					  unsigned long address)
+{
+	return 0;
+}
+
+static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address)
+{
+}
+
+static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+}
+
+static inline void mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+}
+
+static inline void mmu_notifier_mm_init(struct mm_struct *mm)
+{
+}
+
+static inline void mmu_notifier_mm_destroy(struct mm_struct *mm)
+{
+}
+
+#define ptep_clear_flush_young_notify ptep_clear_flush_young
+#define ptep_clear_flush_notify ptep_clear_flush
+
+#endif /* CONFIG_MMU_NOTIFIER */
+
+#endif /* _LINUX_MMU_NOTIFIER_H */
diff -r 082f312bc682 -r 9cf86778092b kernel/fork.c
--- a/kernel/fork.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/kernel/fork.c	Thu Jun 05 17:31:21 2008 +0200
@@ -54,6 +54,7 @@
 #include <linux/tty.h>
 #include <linux/proc_fs.h>
 #include <linux/blkdev.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -386,6 +387,7 @@ static struct mm_struct * mm_init(struct
 
 	if (likely(!mm_alloc_pgd(mm))) {
 		mm->def_flags = 0;
+		mmu_notifier_mm_init(mm);
 		return mm;
 	}
 
@@ -418,6 +420,7 @@ void __mmdrop(struct mm_struct *mm)
 	BUG_ON(mm == &init_mm);
 	mm_free_pgd(mm);
 	destroy_context(mm);
+	mmu_notifier_mm_destroy(mm);
 	free_mm(mm);
 }
 EXPORT_SYMBOL_GPL(__mmdrop);
diff -r 082f312bc682 -r 9cf86778092b mm/Kconfig
--- a/mm/Kconfig	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/Kconfig	Thu Jun 05 17:31:21 2008 +0200
@@ -205,3 +205,6 @@ config VIRT_TO_BUS
 config VIRT_TO_BUS
 	def_bool y
 	depends on !ARCH_NO_VIRT_TO_BUS
+
+config MMU_NOTIFIER
+	bool
diff -r 082f312bc682 -r 9cf86778092b mm/Makefile
--- a/mm/Makefile	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/Makefile	Thu Jun 05 17:31:21 2008 +0200
@@ -33,4 +33,5 @@ obj-$(CONFIG_SMP) += allocpercpu.o
 obj-$(CONFIG_SMP) += allocpercpu.o
 obj-$(CONFIG_QUICKLIST) += quicklist.o
 obj-$(CONFIG_CGROUP_MEM_RES_CTLR) += memcontrol.o
+obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
 
diff -r 082f312bc682 -r 9cf86778092b mm/filemap_xip.c
--- a/mm/filemap_xip.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/filemap_xip.c	Thu Jun 05 17:31:21 2008 +0200
@@ -188,7 +188,7 @@ __xip_unmap (struct address_space * mapp
 		if (pte) {
 			/* Nuke the page table entry. */
 			flush_cache_page(vma, address, pte_pfn(*pte));
-			pteval = ptep_clear_flush(vma, address, pte);
+			pteval = ptep_clear_flush_notify(vma, address, pte);
 			page_remove_rmap(page, vma);
 			dec_mm_counter(mm, file_rss);
 			BUG_ON(pte_dirty(pteval));
diff -r 082f312bc682 -r 9cf86778092b mm/fremap.c
--- a/mm/fremap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/fremap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -15,6 +15,7 @@
 #include <linux/rmap.h>
 #include <linux/module.h>
 #include <linux/syscalls.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/mmu_context.h>
 #include <asm/cacheflush.h>
@@ -214,7 +215,9 @@ asmlinkage long sys_remap_file_pages(uns
 		spin_unlock(&mapping->i_mmap_lock);
 	}
 
+	mmu_notifier_invalidate_range_start(mm, start, start + size);
 	err = populate_range(mm, vma, start, size, pgoff);
+	mmu_notifier_invalidate_range_end(mm, start, start + size);
 	if (!err && !(flags & MAP_NONBLOCK)) {
 		if (unlikely(has_write_lock)) {
 			downgrade_write(&mm->mmap_sem);
diff -r 082f312bc682 -r 9cf86778092b mm/hugetlb.c
--- a/mm/hugetlb.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/hugetlb.c	Thu Jun 05 17:31:21 2008 +0200
@@ -14,6 +14,7 @@
 #include <linux/mempolicy.h>
 #include <linux/cpuset.h>
 #include <linux/mutex.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/page.h>
 #include <asm/pgtable.h>
@@ -823,6 +824,7 @@ void __unmap_hugepage_range(struct vm_ar
 	BUG_ON(start & ~HPAGE_MASK);
 	BUG_ON(end & ~HPAGE_MASK);
 
+	mmu_notifier_invalidate_range_start(mm, start, end);
 	spin_lock(&mm->page_table_lock);
 	for (address = start; address < end; address += HPAGE_SIZE) {
 		ptep = huge_pte_offset(mm, address);
@@ -843,6 +845,7 @@ void __unmap_hugepage_range(struct vm_ar
 	}
 	spin_unlock(&mm->page_table_lock);
 	flush_tlb_range(vma, start, end);
+	mmu_notifier_invalidate_range_end(mm, start, end);
 	list_for_each_entry_safe(page, tmp, &page_list, lru) {
 		list_del(&page->lru);
 		put_page(page);
diff -r 082f312bc682 -r 9cf86778092b mm/memory.c
--- a/mm/memory.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/memory.c	Thu Jun 05 17:31:21 2008 +0200
@@ -51,6 +51,7 @@
 #include <linux/init.h>
 #include <linux/writeback.h>
 #include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/pgalloc.h>
 #include <asm/uaccess.h>
@@ -649,6 +650,7 @@ int copy_page_range(struct mm_struct *ds
 	unsigned long next;
 	unsigned long addr = vma->vm_start;
 	unsigned long end = vma->vm_end;
+	int ret;
 
 	/*
 	 * Don't copy ptes where a page fault will fill them correctly.
@@ -664,17 +666,33 @@ int copy_page_range(struct mm_struct *ds
 	if (is_vm_hugetlb_page(vma))
 		return copy_hugetlb_page_range(dst_mm, src_mm, vma);
 
+	/*
+	 * We need to invalidate the secondary MMU mappings only when
+	 * there could be a permission downgrade on the ptes of the
+	 * parent mm. And a permission downgrade will only happen if
+	 * is_cow_mapping() returns true.
+	 */
+	if (is_cow_mapping(vma->vm_flags))
+		mmu_notifier_invalidate_range_start(src_mm, addr, end);
+
+	ret = 0;
 	dst_pgd = pgd_offset(dst_mm, addr);
 	src_pgd = pgd_offset(src_mm, addr);
 	do {
 		next = pgd_addr_end(addr, end);
 		if (pgd_none_or_clear_bad(src_pgd))
 			continue;
-		if (copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
-						vma, addr, next))
-			return -ENOMEM;
+		if (unlikely(copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
+					    vma, addr, next))) {
+			ret = -ENOMEM;
+			break;
+		}
 	} while (dst_pgd++, src_pgd++, addr = next, addr != end);
-	return 0;
+
+	if (is_cow_mapping(vma->vm_flags))
+		mmu_notifier_invalidate_range_end(src_mm,
+						  vma->vm_start, end);
+	return ret;
 }
 
 static unsigned long zap_pte_range(struct mmu_gather *tlb,
@@ -878,7 +896,9 @@ unsigned long unmap_vmas(struct mmu_gath
 	unsigned long start = start_addr;
 	spinlock_t *i_mmap_lock = details? details->i_mmap_lock: NULL;
 	int fullmm = (*tlbp)->fullmm;
+	struct mm_struct *mm = vma->vm_mm;
 
+	mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
 	for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next) {
 		unsigned long end;
 
@@ -929,6 +949,7 @@ unsigned long unmap_vmas(struct mmu_gath
 		}
 	}
 out:
+	mmu_notifier_invalidate_range_end(mm, start_addr, end_addr);
 	return start;	/* which is now the end (or restart) address */
 }
 
@@ -1561,10 +1582,11 @@ int apply_to_page_range(struct mm_struct
 {
 	pgd_t *pgd;
 	unsigned long next;
-	unsigned long end = addr + size;
+	unsigned long start = addr, end = addr + size;
 	int err;
 
 	BUG_ON(addr >= end);
+	mmu_notifier_invalidate_range_start(mm, start, end);
 	pgd = pgd_offset(mm, addr);
 	do {
 		next = pgd_addr_end(addr, end);
@@ -1572,6 +1594,7 @@ int apply_to_page_range(struct mm_struct
 		if (err)
 			break;
 	} while (pgd++, addr = next, addr != end);
+	mmu_notifier_invalidate_range_end(mm, start, end);
 	return err;
 }
 EXPORT_SYMBOL_GPL(apply_to_page_range);
@@ -1773,7 +1796,7 @@ gotten:
 		 * seen in the presence of one thread doing SMC and another
 		 * thread doing COW.
 		 */
-		ptep_clear_flush(vma, address, page_table);
+		ptep_clear_flush_notify(vma, address, page_table);
 		set_pte_at(mm, address, page_table, entry);
 		update_mmu_cache(vma, address, entry);
 		lru_cache_add_active(new_page);
diff -r 082f312bc682 -r 9cf86778092b mm/mmap.c
--- a/mm/mmap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mmap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -26,6 +26,7 @@
 #include <linux/mount.h>
 #include <linux/mempolicy.h>
 #include <linux/rmap.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
@@ -2048,6 +2049,7 @@ void exit_mmap(struct mm_struct *mm)
 
 	/* mm's last user has gone, and its about to be pulled down */
 	arch_exit_mmap(mm);
+	mmu_notifier_release(mm);
 
 	lru_add_drain();
 	flush_cache_mm(mm);
diff -r 082f312bc682 -r 9cf86778092b mm/mmu_notifier.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mm/mmu_notifier.c	Thu Jun 05 17:31:21 2008 +0200
@@ -0,0 +1,276 @@
+/*
+ *  linux/mm/mmu_notifier.c
+ *
+ *  Copyright (C) 2008  Qumranet, Inc.
+ *  Copyright (C) 2008  SGI
+ *             Christoph Lameter <clameter@sgi.com>
+ *
+ *  This work is licensed under the terms of the GNU GPL, version 2. See
+ *  the COPYING file in the top-level directory.
+ */
+
+#include <linux/mmu_notifier.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/err.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+
+/*
+ * This function can't run concurrently against mmu_notifier_register
+ * because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
+ * runs with mm_users == 0. Other tasks may still invoke mmu notifiers
+ * in parallel despite there being no task using this mm any more,
+ * through the vmas outside of the exit_mmap context, such as with
+ * vmtruncate. This serializes against mmu_notifier_unregister with
+ * the mmu_notifier_mm->lock in addition to RCU and it serializes
+ * against the other mmu notifiers with RCU. struct mmu_notifier_mm
+ * can't go away from under us as exit_mmap holds an mm_count pin
+ * itself.
+ */
+void __mmu_notifier_release(struct mm_struct *mm)
+{
+	struct mmu_notifier *mn;
+
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	while (unlikely(!hlist_empty(&mm->mmu_notifier_mm->list))) {
+		mn = hlist_entry(mm->mmu_notifier_mm->list.first,
+				 struct mmu_notifier,
+				 hlist);
+		/*
+		 * We arrived before mmu_notifier_unregister so
+		 * mmu_notifier_unregister will do nothing other than
+		 * to wait ->release to finish and
+		 * mmu_notifier_unregister to return.
+		 */
+		hlist_del_init_rcu(&mn->hlist);
+		/*
+		 * RCU here will block mmu_notifier_unregister until
+		 * ->release returns.
+		 */
+		rcu_read_lock();
+		spin_unlock(&mm->mmu_notifier_mm->lock);
+		/*
+		 * if ->release runs before mmu_notifier_unregister it
+		 * must be handled as it's the only way for the driver
+		 * to flush all existing sptes and stop the driver
+		 * from establishing any more sptes before all the
+		 * pages in the mm are freed.
+		 */
+		if (mn->ops->release)
+			mn->ops->release(mn, mm);
+		rcu_read_unlock();
+		spin_lock(&mm->mmu_notifier_mm->lock);
+	}
+	spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	/*
+	 * synchronize_rcu here prevents mmu_notifier_release to
+	 * return to exit_mmap (which would proceed freeing all pages
+	 * in the mm) until the ->release method returns, if it was
+	 * invoked by mmu_notifier_unregister.
+	 *
+	 * The mmu_notifier_mm can't go away from under us because one
+	 * mm_count is hold by exit_mmap.
+	 */
+	synchronize_rcu();
+}
+
+/*
+ * If no young bitflag is supported by the hardware, ->clear_flush_young can
+ * unmap the address and return 1 or 0 depending if the mapping previously
+ * existed or not.
+ */
+int __mmu_notifier_clear_flush_young(struct mm_struct *mm,
+					unsigned long address)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+	int young = 0;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->clear_flush_young)
+			young |= mn->ops->clear_flush_young(mn, mm, address);
+	}
+	rcu_read_unlock();
+
+	return young;
+}
+
+void __mmu_notifier_invalidate_page(struct mm_struct *mm,
+					  unsigned long address)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->invalidate_page)
+			mn->ops->invalidate_page(mn, mm, address);
+	}
+	rcu_read_unlock();
+}
+
+void __mmu_notifier_invalidate_range_start(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->invalidate_range_start)
+			mn->ops->invalidate_range_start(mn, mm, start, end);
+	}
+	rcu_read_unlock();
+}
+
+void __mmu_notifier_invalidate_range_end(struct mm_struct *mm,
+				  unsigned long start, unsigned long end)
+{
+	struct mmu_notifier *mn;
+	struct hlist_node *n;
+
+	rcu_read_lock();
+	hlist_for_each_entry_rcu(mn, n, &mm->mmu_notifier_mm->list, hlist) {
+		if (mn->ops->invalidate_range_end)
+			mn->ops->invalidate_range_end(mn, mm, start, end);
+	}
+	rcu_read_unlock();
+}
+
+static int do_mmu_notifier_register(struct mmu_notifier *mn,
+				    struct mm_struct *mm,
+				    int take_mmap_sem)
+{
+	struct mmu_notifier_mm * mmu_notifier_mm;
+	int ret;
+
+	BUG_ON(atomic_read(&mm->mm_users) <= 0);
+
+	ret = -ENOMEM;
+	mmu_notifier_mm = kmalloc(sizeof(struct mmu_notifier_mm), GFP_KERNEL);
+	if (unlikely(!mmu_notifier_mm))
+		goto out;
+
+	if (take_mmap_sem)
+		down_write(&mm->mmap_sem);
+	ret = mm_take_all_locks(mm);
+	if (unlikely(ret))
+		goto out_cleanup;
+
+	if (!mm_has_notifiers(mm)) {
+		INIT_HLIST_HEAD(&mmu_notifier_mm->list);
+		spin_lock_init(&mmu_notifier_mm->lock);
+		mm->mmu_notifier_mm = mmu_notifier_mm;
+		mmu_notifier_mm = NULL;
+	}
+	atomic_inc(&mm->mm_count);
+
+	/*
+	 * Serialize the update against mmu_notifier_unregister. A
+	 * side note: mmu_notifier_release can't run concurrently with
+	 * us because we hold the mm_users pin (either implicitly as
+	 * current->mm or explicitly with get_task_mm() or similar).
+	 * We can't race against any other mmu notifier method either
+	 * thanks to mm_take_all_locks().
+	 */
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	hlist_add_head(&mn->hlist, &mm->mmu_notifier_mm->list);
+	spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	mm_drop_all_locks(mm);
+out_cleanup:
+	if (take_mmap_sem)
+		up_write(&mm->mmap_sem);
+	/* kfree() does nothing if mmu_notifier_mm is NULL */
+	kfree(mmu_notifier_mm);
+out:
+	BUG_ON(atomic_read(&mm->mm_users) <= 0);
+	return ret;
+}
+
+/*
+ * Must not hold mmap_sem nor any other VM related lock when calling
+ * this registration function. Must also ensure mm_users can't go down
+ * to zero while this runs to avoid races with mmu_notifier_release,
+ * so mm has to be current->mm or the mm should be pinned safely such
+ * as with get_task_mm(). If the mm is not current->mm, the mm_users
+ * pin should be released by calling mmput after mmu_notifier_register
+ * returns. mmu_notifier_unregister must be always called to
+ * unregister the notifier. mm_count is automatically pinned to allow
+ * mmu_notifier_unregister to safely run at any time later, before or
+ * after exit_mmap. ->release will always be called before exit_mmap
+ * frees the pages.
+ */
+int mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	return do_mmu_notifier_register(mn, mm, 1);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_register);
+
+/*
+ * Same as mmu_notifier_register but here the caller must hold the
+ * mmap_sem in write mode.
+ */
+int __mmu_notifier_register(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	return do_mmu_notifier_register(mn, mm, 0);
+}
+EXPORT_SYMBOL_GPL(__mmu_notifier_register);
+
+/* this is called after the last mmu_notifier_unregister() returned */
+void __mmu_notifier_mm_destroy(struct mm_struct *mm)
+{
+	BUG_ON(!hlist_empty(&mm->mmu_notifier_mm->list));
+	kfree(mm->mmu_notifier_mm);
+	mm->mmu_notifier_mm = LIST_POISON1; /* debug */
+}
+
+/*
+ * This releases the mm_count pin automatically and frees the mm
+ * structure if it was the last user of it. It serializes against
+ * running mmu notifiers with RCU and against mmu_notifier_unregister
+ * with the unregister lock + RCU. All sptes must be dropped before
+ * calling mmu_notifier_unregister. ->release or any other notifier
+ * method may be invoked concurrently with mmu_notifier_unregister,
+ * and only after mmu_notifier_unregister returned we're guaranteed
+ * that ->release or any other method can't run anymore.
+ */
+void mmu_notifier_unregister(struct mmu_notifier *mn, struct mm_struct *mm)
+{
+	BUG_ON(atomic_read(&mm->mm_count) <= 0);
+
+	spin_lock(&mm->mmu_notifier_mm->lock);
+	if (!hlist_unhashed(&mn->hlist)) {
+		hlist_del_rcu(&mn->hlist);
+
+		/*
+		 * RCU here will force exit_mmap to wait ->release to finish
+		 * before freeing the pages.
+		 */
+		rcu_read_lock();
+		spin_unlock(&mm->mmu_notifier_mm->lock);
+		/*
+		 * exit_mmap will block in mmu_notifier_release to
+		 * guarantee ->release is called before freeing the
+		 * pages.
+		 */
+		if (mn->ops->release)
+			mn->ops->release(mn, mm);
+		rcu_read_unlock();
+	} else
+		spin_unlock(&mm->mmu_notifier_mm->lock);
+
+	/*
+	 * Wait any running method to finish, of course including
+	 * ->release if it was run by mmu_notifier_relase instead of us.
+	 */
+	synchronize_rcu();
+
+	BUG_ON(atomic_read(&mm->mm_count) <= 0);
+
+	mmdrop(mm);
+}
+EXPORT_SYMBOL_GPL(mmu_notifier_unregister);
diff -r 082f312bc682 -r 9cf86778092b mm/mprotect.c
--- a/mm/mprotect.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mprotect.c	Thu Jun 05 17:31:21 2008 +0200
@@ -21,6 +21,7 @@
 #include <linux/syscalls.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
+#include <linux/mmu_notifier.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
 #include <asm/cacheflush.h>
@@ -207,10 +208,12 @@ success:
 		dirty_accountable = 1;
 	}
 
+	mmu_notifier_invalidate_range_start(mm, start, end);
 	if (is_vm_hugetlb_page(vma))
 		hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 	else
 		change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
+	mmu_notifier_invalidate_range_end(mm, start, end);
 	vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 	vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 	return 0;
diff -r 082f312bc682 -r 9cf86778092b mm/mremap.c
--- a/mm/mremap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/mremap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -18,6 +18,7 @@
 #include <linux/highmem.h>
 #include <linux/security.h>
 #include <linux/syscalls.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/uaccess.h>
 #include <asm/cacheflush.h>
@@ -74,7 +75,11 @@ static void move_ptes(struct vm_area_str
 	struct mm_struct *mm = vma->vm_mm;
 	pte_t *old_pte, *new_pte, pte;
 	spinlock_t *old_ptl, *new_ptl;
+	unsigned long old_start;
 
+	old_start = old_addr;
+	mmu_notifier_invalidate_range_start(vma->vm_mm,
+					    old_start, old_end);
 	if (vma->vm_file) {
 		/*
 		 * Subtle point from Rajesh Venkatasubramanian: before
@@ -116,6 +121,7 @@ static void move_ptes(struct vm_area_str
 	pte_unmap_unlock(old_pte - 1, old_ptl);
 	if (mapping)
 		spin_unlock(&mapping->i_mmap_lock);
+	mmu_notifier_invalidate_range_end(vma->vm_mm, old_start, old_end);
 }
 
 #define LATENCY_LIMIT	(64 * PAGE_SIZE)
diff -r 082f312bc682 -r 9cf86778092b mm/rmap.c
--- a/mm/rmap.c	Thu Jun 05 17:30:17 2008 +0200
+++ b/mm/rmap.c	Thu Jun 05 17:31:21 2008 +0200
@@ -49,6 +49,7 @@
 #include <linux/module.h>
 #include <linux/kallsyms.h>
 #include <linux/memcontrol.h>
+#include <linux/mmu_notifier.h>
 
 #include <asm/tlbflush.h>
 
@@ -287,7 +288,7 @@ static int page_referenced_one(struct pa
 	if (vma->vm_flags & VM_LOCKED) {
 		referenced++;
 		*mapcount = 1;	/* break early from loop */
-	} else if (ptep_clear_flush_young(vma, address, pte))
+	} else if (ptep_clear_flush_young_notify(vma, address, pte))
 		referenced++;
 
 	/* Pretend the page is referenced if the task has the
@@ -457,7 +458,7 @@ static int page_mkclean_one(struct page 
 		pte_t entry;
 
 		flush_cache_page(vma, address, pte_pfn(*pte));
-		entry = ptep_clear_flush(vma, address, pte);
+		entry = ptep_clear_flush_notify(vma, address, pte);
 		entry = pte_wrprotect(entry);
 		entry = pte_mkclean(entry);
 		set_pte_at(mm, address, pte, entry);
@@ -717,14 +718,14 @@ static int try_to_unmap_one(struct page 
 	 * skipped over this mm) then we should reactivate it.
 	 */
 	if (!migration && ((vma->vm_flags & VM_LOCKED) ||
-			(ptep_clear_flush_young(vma, address, pte)))) {
+			(ptep_clear_flush_young_notify(vma, address, pte)))) {
 		ret = SWAP_FAIL;
 		goto out_unmap;
 	}
 
 	/* Nuke the page table entry. */
 	flush_cache_page(vma, address, page_to_pfn(page));
-	pteval = ptep_clear_flush(vma, address, pte);
+	pteval = ptep_clear_flush_notify(vma, address, pte);
 
 	/* Move the dirty bit to the physical page now the pte is gone. */
 	if (pte_dirty(pteval))
@@ -849,12 +850,12 @@ static void try_to_unmap_cluster(unsigne
 		page = vm_normal_page(vma, address, *pte);
 		BUG_ON(!page || PageAnon(page));
 
-		if (ptep_clear_flush_young(vma, address, pte))
+		if (ptep_clear_flush_young_notify(vma, address, pte))
 			continue;
 
 		/* Nuke the page table entry. */
 		flush_cache_page(vma, address, pte_pfn(*pte));
-		pteval = ptep_clear_flush(vma, address, pte);
+		pteval = ptep_clear_flush_notify(vma, address, pte);
 
 		/* If nonlinear, store the file page offset in the pte. */
 		if (page->index != linear_page_index(vma, address))