[PATCH v4 19/27] userfaultfd: introduce helper vma_find_uffd

[Peter Xu]

We've have multiple (and more coming) places that would like to find a
userfault enabled VMA from a mm struct that covers a specific memory
range.  This patch introduce the helper for it, meanwhile apply it to
the code.

Suggested-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Jerome Glisse <jglisse@xxxxxxxxxx>
Reviewed-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
 mm/userfaultfd.c | 54 +++++++++++++++++++++++++++---------------------
 1 file changed, 30 insertions(+), 24 deletions(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 240de2a8492d..2606409572b2 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -20,6 +20,34 @@
 #include <asm/tlbflush.h>
 #include "internal.h"
 
+/*
+ * Find a valid userfault enabled VMA region that covers the whole
+ * address range, or NULL on failure.  Must be called with mmap_sem
+ * held.
+ */
+static struct vm_area_struct *vma_find_uffd(struct mm_struct *mm,
+					    unsigned long start,
+					    unsigned long len)
+{
+	struct vm_area_struct *vma = find_vma(mm, start);
+
+	if (!vma)
+		return NULL;
+
+	/*
+	 * Check the vma is registered in uffd, this is required to
+	 * enforce the VM_MAYWRITE check done at uffd registration
+	 * time.
+	 */
+	if (!vma->vm_userfaultfd_ctx.ctx)
+		return NULL;
+
+	if (start < vma->vm_start || start + len > vma->vm_end)
+		return NULL;
+
+	return vma;
+}
+
 static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 			    pmd_t *dst_pmd,
 			    struct vm_area_struct *dst_vma,
@@ -228,20 +256,9 @@ static __always_inline ssize_t __mcopy_atomic_hugetlb(struct mm_struct *dst_mm,
 	 */
 	if (!dst_vma) {
 		err = -ENOENT;
-		dst_vma = find_vma(dst_mm, dst_start);
+		dst_vma = vma_find_uffd(dst_mm, dst_start, len);
 		if (!dst_vma || !is_vm_hugetlb_page(dst_vma))
 			goto out_unlock;
-		/*
-		 * Check the vma is registered in uffd, this is
-		 * required to enforce the VM_MAYWRITE check done at
-		 * uffd registration time.
-		 */
-		if (!dst_vma->vm_userfaultfd_ctx.ctx)
-			goto out_unlock;
-
-		if (dst_start < dst_vma->vm_start ||
-		    dst_start + len > dst_vma->vm_end)
-			goto out_unlock;
 
 		err = -EINVAL;
 		if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
@@ -488,20 +505,9 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
 	 * both valid and fully within a single existing vma.
 	 */
 	err = -ENOENT;
-	dst_vma = find_vma(dst_mm, dst_start);
+	dst_vma = vma_find_uffd(dst_mm, dst_start, len);
 	if (!dst_vma)
 		goto out_unlock;
-	/*
-	 * Check the vma is registered in uffd, this is required to
-	 * enforce the VM_MAYWRITE check done at uffd registration
-	 * time.
-	 */
-	if (!dst_vma->vm_userfaultfd_ctx.ctx)
-		goto out_unlock;
-
-	if (dst_start < dst_vma->vm_start ||
-	    dst_start + len > dst_vma->vm_end)
-		goto out_unlock;
 
 	err = -EINVAL;
 	/*
-- 
2.17.1