remap_file_pages: Use vma_lookup() instead of find_vma()

Using vma_lookup() verifies the start address is contained in the found vma.
This results in easier to read code.

Link: https://lkml.kernel.org/r/20210817135234.1550204-1-Liam.Howlett@oracle.comSigned-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -2994,14 +2994,11 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
 	if (mmap_write_lock_killable(mm))
 		return -EINTR;
 
-	vma = find_vma(mm, start);
+	vma = vma_lookup(mm, start);
 
 	if (!vma || !(vma->vm_flags & VM_SHARED))
 		goto out;
 
-	if (start < vma->vm_start)
-		goto out;
-
 	if (start + size > vma->vm_end) {
 		struct vm_area_struct *next;