mm/hmm: invalidate device page table at start of invalidation

Invalidate device page table at start of invalidation and invalidate in
progress CPU page table snapshooting at both start and end of any
invalidation.

This is helpful when device need to dirty page because the device page
table report the page as dirty.  Dirtying page must happen in the start
mmu notifier callback and not in the end one.

Link: http://lkml.kernel.org/r/20181019160442.18723-7-jglisse@redhat.com
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hmm.c

@@ -43,7 +43,6 @@ static const struct mmu_notifier_ops hmm_mmu_notifier_ops;
  *
  * @mm: mm struct this HMM struct is bound to
  * @lock: lock protecting ranges list
- * @sequence: we track updates to the CPU page table with a sequence number
  * @ranges: list of range being snapshotted
  * @mirrors: list of mirrors for this mm
  * @mmu_notifier: mmu notifier to track updates to CPU page table
@@ -52,7 +51,6 @@ static const struct mmu_notifier_ops hmm_mmu_notifier_ops;
 struct hmm {
 	struct mm_struct	*mm;
 	spinlock_t		lock;
-	atomic_t		sequence;
 	struct list_head	ranges;
 	struct list_head	mirrors;
 	struct mmu_notifier	mmu_notifier;
@@ -85,7 +83,6 @@ static struct hmm *hmm_register(struct mm_struct *mm)
 		return NULL;
 	INIT_LIST_HEAD(&hmm->mirrors);
 	init_rwsem(&hmm->mirrors_sem);
-	atomic_set(&hmm->sequence, 0);
 	hmm->mmu_notifier.ops = NULL;
 	INIT_LIST_HEAD(&hmm->ranges);
 	spin_lock_init(&hmm->lock);
@@ -126,7 +123,7 @@ void hmm_mm_destroy(struct mm_struct *mm)
 	kfree(mm->hmm);
 }
 
-static int hmm_invalidate_range(struct hmm *hmm,
+static int hmm_invalidate_range(struct hmm *hmm, bool device,
 				const struct hmm_update *update)
 {
 	struct hmm_mirror *mirror;
@@ -147,6 +144,9 @@ static int hmm_invalidate_range(struct hmm *hmm,
 	}
 	spin_unlock(&hmm->lock);
 
+	if (!device)
+		return 0;
+
 	down_read(&hmm->mirrors_sem);
 	list_for_each_entry(mirror, &hmm->mirrors, list) {
 		int ret;
@@ -189,18 +189,21 @@ static void hmm_release(struct mmu_notifier *mn, struct mm_struct *mm)
 }
 
 static int hmm_invalidate_range_start(struct mmu_notifier *mn,
-				       struct mm_struct *mm,
-				       unsigned long start,
-				       unsigned long end,
-				       bool blockable)
+				      struct mm_struct *mm,
+				      unsigned long start,
+				      unsigned long end,
+				      bool blockable)
 {
+	struct hmm_update update;
 	struct hmm *hmm = mm->hmm;
 
 	VM_BUG_ON(!hmm);
 
-	atomic_inc(&hmm->sequence);
-
-	return 0;
+	update.start = start;
+	update.end = end;
+	update.event = HMM_UPDATE_INVALIDATE;
+	update.blockable = blockable;
+	return hmm_invalidate_range(hmm, true, &update);
 }
 
 static void hmm_invalidate_range_end(struct mmu_notifier *mn,
@@ -217,7 +220,7 @@ static void hmm_invalidate_range_end(struct mmu_notifier *mn,
 	update.end = end;
 	update.event = HMM_UPDATE_INVALIDATE;
 	update.blockable = true;
-	hmm_invalidate_range(hmm, &update);
+	hmm_invalidate_range(hmm, false, &update);
 }
 
 static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {