From patchwork Mon Apr 22 22:33:02 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Saeed Mahameed X-Patchwork-Id: 1088959 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=none (mailfrom) smtp.mailfrom=vger.kernel.org (client-ip=209.132.180.67; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=fail (p=none dis=none) header.from=mellanox.com Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 44p1hj6rprz9s7T for ; Tue, 23 Apr 2019 08:39:01 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730356AbfDVWjA (ORCPT ); Mon, 22 Apr 2019 18:39:00 -0400 Received: from mail-il-dmz.mellanox.com ([193.47.165.129]:57093 "EHLO mellanox.co.il" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730302AbfDVWi6 (ORCPT ); Mon, 22 Apr 2019 18:38:58 -0400 Received: from Internal Mail-Server by MTLPINE1 (envelope-from saeedm@mellanox.com) with ESMTPS (AES256-SHA encrypted); 23 Apr 2019 01:38:56 +0300 Received: from sx1.mtl.com ([172.16.5.39]) by labmailer.mlnx (8.13.8/8.13.8) with ESMTP id x3MMcQB4021096; Tue, 23 Apr 2019 01:38:54 +0300 From: Saeed Mahameed To: "David S. Miller" Cc: netdev@vger.kernel.org, Jesper Dangaard Brouer , Jonathan Lemon , Maxim Mikityanskiy , Tariq Toukan , Saeed Mahameed Subject: [net-next 10/14] net/mlx5e: Add an underflow warning comment Date: Mon, 22 Apr 2019 15:33:02 -0700 Message-Id: <20190422223306.31568-11-saeedm@mellanox.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190422223306.31568-1-saeedm@mellanox.com> References: <20190422223306.31568-1-saeedm@mellanox.com> MIME-Version: 1.0 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Maxim Mikityanskiy mlx5e_mpwqe_get_log_rq_size calculates the number of WQEs (N) based on the requested number of frames in the RQ (F) and the number of packets per WQE (P). It ensures that N is not less than the minimum number of WQEs in an RQ (N_min). Arithmetically, it means that F / P >= N_min should be true. This function deals with logarithms, so it should check that log(F) - log(P) >= log(N_min). However, if F < P, this expression will cause an unsigned underflow. Check log(F) >= log(P) + log(N_min) instead. Signed-off-by: Maxim Mikityanskiy Reviewed-by: Tariq Toukan Signed-off-by: Saeed Mahameed --- drivers/net/ethernet/mellanox/mlx5/core/en/params.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c index 658337c3bba1..fa6661ea6310 100644 --- a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c @@ -62,11 +62,14 @@ bool mlx5e_rx_mpwqe_is_linear_skb(struct mlx5_core_dev *mdev, u8 mlx5e_mpwqe_get_log_rq_size(struct mlx5e_params *params) { + u8 log_pkts_per_wqe = mlx5e_mpwqe_log_pkts_per_wqe(params); + + /* Numbers are unsigned, don't subtract to avoid underflow. */ if (params->log_rq_mtu_frames < - mlx5e_mpwqe_log_pkts_per_wqe(params) + MLX5E_PARAMS_MINIMUM_LOG_RQ_SIZE_MPW) + log_pkts_per_wqe + MLX5E_PARAMS_MINIMUM_LOG_RQ_SIZE_MPW) return MLX5E_PARAMS_MINIMUM_LOG_RQ_SIZE_MPW; - return params->log_rq_mtu_frames - mlx5e_mpwqe_log_pkts_per_wqe(params); + return params->log_rq_mtu_frames - log_pkts_per_wqe; } u8 mlx5e_mpwqe_get_log_stride_size(struct mlx5_core_dev *mdev,