mm/migrate: use vma_lookup() in do_pages_stat_array()

Use vma_lookup() to find the VMA at a specific address.  As vma_lookup()
will return NULL if the address is not within any VMA, the start address
no longer needs to be validated.

Link: https://lkml.kernel.org/r/20210521174745.2219620-20-Liam.Howlett@Oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: Laurent Dufour <ldufour@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/migrate.c

@@ -1834,8 +1834,8 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
 		struct page *page;
 		int err = -EFAULT;
 
-		vma = find_vma(mm, addr);
-		if (!vma || addr < vma->vm_start)
+		vma = vma_lookup(mm, addr);
+		if (!vma)
 			goto set_status;
 
 		/* FOLL_DUMP to ignore special (like zero) pages */