mm/hugetlb.c: call MMU notifiers when copying a hugetlb page range

When copy_hugetlb_page_range() is called to copy a range of hugetlb
mappings, the secondary MMUs are not notified if there is a protection
downgrade, which breaks COW semantics in KVM.

This patch adds the necessary MMU notifier calls.

Signed-off-by: Andreas Sandberg <[e-mail]>
Acked-by: Steve Capper <[e-mail]>
Acked-by: Marc Zyngier <[e-mail]>
Cc: Mel Gorman <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/hugetlb.c

···
 	int cow;
 	struct hstate *h = hstate_vma(vma);
 	unsigned long sz = huge_page_size(h);
+	unsigned long mmun_start;	/* For mmu_notifiers */
+	unsigned long mmun_end;		/* For mmu_notifiers */
+	int ret = 0;
 
 	cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
+
+	mmun_start = vma->vm_start;
+	mmun_end = vma->vm_end;
+	if (cow)
+		mmu_notifier_invalidate_range_start(src, mmun_start, mmun_end);
 
 	for (addr = vma->vm_start; addr < vma->vm_end; addr += sz) {
 		spinlock_t *src_ptl, *dst_ptl;
···
 		if (!src_pte)
 			continue;
 		dst_pte = huge_pte_alloc(dst, addr, sz);
-		if (!dst_pte)
-			goto nomem;
+		if (!dst_pte) {
+			ret = -ENOMEM;
+			break;
+		}
 
 		/* If the pagetables are shared don't copy or take references */
 		if (dst_pte == src_pte)
···
 		spin_unlock(src_ptl);
 		spin_unlock(dst_ptl);
 	}
-	return 0;
 
-nomem:
-	return -ENOMEM;
+	if (cow)
+		mmu_notifier_invalidate_range_end(src, mmun_start, mmun_end);
+
+	return ret;
 }
 
 static int is_hugetlb_entry_migration(pte_t pte)