misc/sgi-gru/grufault: use vma_lookup() in gru_find_vma()

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/20210521174745.2219620-16-Liam.Howlett@Oracle.comSigned-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>

drivers/misc/sgi-gru/grufault.c

@@ -49,8 +49,8 @@ struct vm_area_struct *gru_find_vma(unsigned long vaddr)
 {
 	struct vm_area_struct *vma;
 
-	vma = find_vma(current->mm, vaddr);
-	if (vma && vma->vm_start <= vaddr && vma->vm_ops == &gru_vm_ops)
+	vma = vma_lookup(current->mm, vaddr);
+	if (vma && vma->vm_ops == &gru_vm_ops)
 		return vma;
 	return NULL;
 }