dm verity: use bvec_kmap_local in verity_for_bv_block

Using local kmaps slightly reduces the chances to stray writes, and
the bvec interface cleans up the code a little bit.

Signed-off-by: Christoph Hellwig <[email protected]>
Signed-off-by: Mike Snitzer <[email protected]>

Author: Christoph Hellwig

drivers/md/dm-verity-target.c

@@ -427,14 +427,14 @@ int verity_for_bv_block(struct dm_verity *v, struct dm_verity_io *io,
 		unsigned len;
 		struct bio_vec bv = bio_iter_iovec(bio, *iter);
 
-		page = kmap_atomic(bv.bv_page);
+		page = bvec_kmap_local(&bv);
 		len = bv.bv_len;
 
 		if (likely(len >= todo))
 			len = todo;
 
-		r = process(v, io, page + bv.bv_offset, len);
-		kunmap_atomic(page);
+		r = process(v, io, page, len);
+		kunmap_local(page);
 
 		if (r < 0)
 			return r;