[PATCH] mm: Call MMU notifiers when copying a hugetlb page range

[PATCH] mm: Call MMU notifiers when copying a hugetlb page range

[Andreas Sandberg]

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 <andreas@sandberg.pp.se>
Acked-by: Steve Capper <steve.capper@linaro.org>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
---
 mm/hugetlb.c |   21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0b7656e..f5c5002 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2372,16 +2372,26 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
 	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;
 
+	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) {
 		src_pte = huge_pte_offset(src, addr);
 		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)
@@ -2401,10 +2411,11 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
 		spin_unlock(&src->page_table_lock);
 		spin_unlock(&dst->page_table_lock);
 	}
-	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)
-- 
1.7.9.5

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