vringh: use bvec_kmap_local

Use the bvec_kmap_local helper rather than digging into the bvec
internals.

Signed-off-by: Christoph Hellwig <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>
Reviewed-by: Chaitanya Kulkarni <[e-mail]>

drivers/vhost/vringh.c

···
 		if (ret)
 			return ret;
 	} else {
-		void *kaddr = kmap_local_page(ivec.iov.bvec[0].bv_page);
-		void *from = kaddr + ivec.iov.bvec[0].bv_offset;
+		__virtio16 *from = bvec_kmap_local(&ivec.iov.bvec[0]);
 
-		tmp = READ_ONCE(*(__virtio16 *)from);
-		kunmap_local(kaddr);
+		tmp = READ_ONCE(*from);
+		kunmap_local(from);
 	}
 
 	*val = vringh16_to_cpu(vrh, tmp);
···
 		if (ret)
 			return ret;
 	} else {
-		void *kaddr = kmap_local_page(ivec.iov.bvec[0].bv_page);
-		void *to = kaddr + ivec.iov.bvec[0].bv_offset;
+		__virtio16 *to = bvec_kmap_local(&ivec.iov.bvec[0]);
 
-		WRITE_ONCE(*(__virtio16 *)to, tmp);
-		kunmap_local(kaddr);
+		WRITE_ONCE(*to, tmp);
+		kunmap_local(to);
 	}
 
 	return 0;