mm/pagewalk: don't trigger test_walk() in walk_page_vma()

As Peter points out, the caller passes a single VMA and can just do that
check itself.

And in fact, no existing users rely on test_walk() getting called. So
let's just remove it and make the implementation slightly more efficient.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: David Hildenbrand <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Jason Gunthorpe <[e-mail]>
Cc: John Hubbard <[e-mail]>
Cc: Matthew Wilcox (Oracle) <[e-mail]>
Cc: Peter Xu <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/pagewalk.h

···
  *			"do page table walk over the current vma", returning
  *			a negative value means "abort current page table walk
  *			right now" and returning 1 means "skip the current vma"
+ *			Note that this callback is not called when the caller
+ *			passes in a single VMA as for walk_page_vma().
  * @pre_vma:            if set, called before starting walk on a non-null vma.
  * @post_vma:           if set, called after a walk on a non-null vma, provided
  *                      that @pre_vma and the vma walk succeeded.

mm/pagewalk.c

···
 		.vma		= vma,
 		.private	= private,
 	};
-	int err;
 
 	if (!walk.mm)
 		return -EINVAL;
 
 	mmap_assert_locked(walk.mm);
-
-	err = walk_page_test(vma->vm_start, vma->vm_end, &walk);
-	if (err > 0)
-		return 0;
-	if (err < 0)
-		return err;
 	return __walk_page_range(vma->vm_start, vma->vm_end, &walk);
 }