From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net] net/mlx4_en: Don't reuse RX page when XDP is set Date: Mon, 16 Jul 2018 14:08:33 -0700 (PDT) Message-ID: <20180716.140833.1871284102811541207.davem@davemloft.net> References: <1531652079-27380-1-git-send-email-tariqt@mellanox.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, eranbe@mellanox.com, kafai@fb.com, saeedm@mellanox.com, edumazet@google.com To: tariqt@mellanox.com Return-path: Received: from shards.monkeyblade.net ([23.128.96.9]:60220 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728412AbeGPVhp (ORCPT ); Mon, 16 Jul 2018 17:37:45 -0400 In-Reply-To: <1531652079-27380-1-git-send-email-tariqt@mellanox.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Tariq Toukan Date: Sun, 15 Jul 2018 13:54:39 +0300 > From: Saeed Mahameed > > When a new rx packet arrives, the rx path will decide whether to reuse > the remainder of the page or not according to one of the below conditions: > 1. frag_info->frag_stride == PAGE_SIZE / 2 > 2. frags->page_offset + frag_info->frag_size > PAGE_SIZE; > > The first condition is no met for when XDP is set. > For XDP, page_offset is always set to priv->rx_headroom which is > XDP_PACKET_HEADROOM and frag_info->frag_size is around mtu size + some > padding, still the 2nd release condition will hold since > XDP_PACKET_HEADROOM + 1536 < PAGE_SIZE, as a result the page will not > be released and will be _wrongly_ reused for next free rx descriptor. > > In XDP there is an assumption to have a page per packet and reuse can > break such assumption and might cause packet data corruptions. > > Fix this by adding an extra condition (!priv->rx_headroom) to the 2nd > case to avoid page reuse when XDP is set, since rx_headroom is set to 0 > for non XDP setup and set to XDP_PACKET_HEADROOM for XDP setup. > > No additional cache line is required for the new condition. > > Fixes: 34db548bfb95 ("mlx4: add page recycling in receive path") > Signed-off-by: Saeed Mahameed > Signed-off-by: Tariq Toukan > Suggested-by: Martin KaFai Lau Applied and queued up for -stable.