RDMA/uverbs: Optimize clearing of extra bytes in response

Clear extra bytes in response in batch manner instead
of doing it per-byte.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Yuval Shaia <yuval.shaia@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/uverbs_cmd.c

@@ -58,19 +58,21 @@
 static int uverbs_response(struct uverbs_attr_bundle *attrs, const void *resp,
 			   size_t resp_len)
 {
-	u8 __user *cur = attrs->ucore.outbuf + resp_len;
-	u8 __user *end = attrs->ucore.outbuf + attrs->ucore.outlen;
 	int ret;
 
 	if (copy_to_user(attrs->ucore.outbuf, resp,
 			 min(attrs->ucore.outlen, resp_len)))
 		return -EFAULT;
 
-	/* Zero fill any extra memory that user space might have provided */
-	for (; cur < end; cur++) {
-		ret = put_user(0, cur);
+	if (resp_len < attrs->ucore.outlen) {
+		/*
+		 * Zero fill any extra memory that user
+		 * space might have provided.
+		 */
+		ret = clear_user(attrs->ucore.outbuf + resp_len,
+				 attrs->ucore.outlen - resp_len);
 		if (ret)
-			return ret;
+			return -EFAULT;
 	}
 
 	return 0;