1 files changed, 19 insertions, 38 deletions

diff --git a/mm/gup.c b/mm/gup.c
index a9d4d724aef7..7bc1ba9ce440 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1729,11 +1729,11 @@ EXPORT_SYMBOL(fault_in_writeable);
  * @uaddr: start of address range
  * @size: length of address range
  *
- * Faults in an address range using get_user_pages, i.e., without triggering
- * hardware page faults.  This is primarily useful when we already know that
- * some or all of the pages in the address range aren't in memory.
+ * Faults in an address range for writing.  This is primarily useful when we
+ * already know that some or all of the pages in the address range aren't in
+ * memory.
  *
- * Other than fault_in_writeable(), this function is non-destructive.
+ * Unlike fault_in_writeable(), this function is non-destructive.
  *
  * Note that we don't pin or otherwise hold the pages referenced that we fault
  * in.  There's no guarantee that they'll stay in memory for any duration of
@@ -1744,46 +1744,27 @@ EXPORT_SYMBOL(fault_in_writeable);
  */
 size_t fault_in_safe_writeable(const char __user *uaddr, size_t size)
 {
-	unsigned long start = (unsigned long)untagged_addr(uaddr);
-	unsigned long end, nstart, nend;
+	unsigned long start = (unsigned long)uaddr, end;
 	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma = NULL;
-	int locked = 0;
+	bool unlocked = false;
 
-	nstart = start & PAGE_MASK;
+	if (unlikely(size == 0))
+		return 0;
 	end = PAGE_ALIGN(start + size);
-	if (end < nstart)
+	if (end < start)
 		end = 0;
-	for (; nstart != end; nstart = nend) {
-		unsigned long nr_pages;
-		long ret;
 
-		if (!locked) {
-			locked = 1;
-			mmap_read_lock(mm);
-			vma = find_vma(mm, nstart);
-		} else if (nstart >= vma->vm_end)
-			vma = vma->vm_next;
-		if (!vma || vma->vm_start >= end)
-			break;
-		nend = end ? min(end, vma->vm_end) : vma->vm_end;
-		if (vma->vm_flags & (VM_IO | VM_PFNMAP))
-			continue;
-		if (nstart < vma->vm_start)
-			nstart = vma->vm_start;
-		nr_pages = (nend - nstart) / PAGE_SIZE;
-		ret = __get_user_pages_locked(mm, nstart, nr_pages,
-					      NULL, NULL, &locked,
-					      FOLL_TOUCH | FOLL_WRITE);
-		if (ret <= 0)
+	mmap_read_lock(mm);
+	do {
+		if (fixup_user_fault(mm, start, FAULT_FLAG_WRITE, &unlocked))
 			break;
-		nend = nstart + ret * PAGE_SIZE;
-	}
-	if (locked)
-		mmap_read_unlock(mm);
-	if (nstart == end)
-		return 0;
-	return size - min_t(size_t, nstart - start, size);
+		start = (start + PAGE_SIZE) & PAGE_MASK;
+	} while (start != end);
+	mmap_read_unlock(mm);
+
+	if (size > (unsigned long)uaddr - start)
+		return size - ((unsigned long)uaddr - start);
+	return 0;
 }
 EXPORT_SYMBOL(fault_in_safe_writeable);