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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Khalid Manaa , Ben Ben-Ishay Cc: horms@kernel.org, netdev@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260729204745.166584-1-cosmosocket@gmail.com> Content-Language: en-US From: Dragos Tatulea In-Reply-To: <20260729204745.166584-1-cosmosocket@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR4P281CA0192.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:ca::10) To CH3PR12MB8728.namprd12.prod.outlook.com (2603:10b6:610:171::12) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PR12MB8728:EE_|DS2PR12MB9797:EE_ X-MS-Office365-Filtering-Correlation-Id: 0e79989a-9689-435d-54a1-08deee6406a5 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|23010399003|7416014|376014|1800799024|921020|6133799003|22082099003|18002099003|56012099006|10067099003|5023799004|11063799006; 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It is a good find. On 29.07.26 22:47, Tianyu Zuo wrote: > mlx5e_hw_gro_skb_has_enough_space() bounds a HW GRO session by the > payload held in the skb fragments only. The L3/L4 headers that > header-data split placed in the linear area are not accounted for, and > the limit is inclusive of GRO_LEGACY_MAX_SIZE. > > On a 4K page system a session can therefore grow to 16 full page > fragments (65536 bytes) plus the 40 bytes of IPv4/TCP headers in the > linear part, giving skb->len = 65576. > > mlx5e_shampo_update_hdr() writes the IP length itself: > > __be16 newlen = htons(skb->len - nhoff); > csum_replace2(&ipv4->check, ipv4->tot_len, newlen); > ipv4->tot_len = newlen; > Commit message is clear until here. > With nhoff == 0 this stores tot_len = 40 and updates the header checksum > to match, so the corruption is self-consistent. The GRO stack does not > repair it: the header is written before napi_gro_receive(), and > inet_gro_complete() only runs for skbs that the GRO engine holds on its > gro_list. HW GRO sessions are typically flushed on TCP_FLAG_PSH, which > makes tcp_gro_receive() set NAPI_GRO_CB(skb)->flush, so dev_gro_receive() > hands the skb over via GRO_NORMAL and the gro_complete() callbacks are > never invoked. The length check in inet_gro_receive() cannot catch it > either, since tot_len and skb_gro_len() are compared modulo 64K. > > ip_rcv_core() then trims the 64KB skb down to the wrapped tot_len, > silently dropping the payload. The IPv6 path wraps identically in > ipv6hdr->payload_len. > > Triggering this requires the payload of the aggregated session to reach > GRO_LEGACY_MAX_SIZE with every fragment fully populated, since > page_size * nr_frags otherwise overestimates the data actually present > and the session is flushed earlier. In practice this needs an MSS that > is a multiple of the page size (for example 8192 on a 4K page host with > jumbo frames) together with a page aligned start of the session. > You can drop this bit. > Account for skb_headlen() and make both checks strictly less than > GRO_LEGACY_MAX_SIZE so that skb->len can never exceed 65535. > This is useful. > The check is strictly more conservative than before, so the implicit > bound on the fragment count is preserved: page_size * nr_frags + > data_bcnt <= 65535 gives nr_frags + data_bcnt / page_size <= > 65536 / page_size - 1, and a single CQE adds at most > data_bcnt / page_size + 1 fragments, for a total of at most > 65536 / page_size (16 on 4K pages), well below MAX_SKB_FRAGS. > You can drop this last paragraph. Or summarize it in the previous one. > Fixes: 92552d3abd32 ("net/mlx5e: HW_GRO cqe handler implementation") > Signed-off-by: Tianyu Zuo > --- > drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > index 6fbc0441c4b8..2e9676305439 100644 > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c > @@ -2222,9 +2222,10 @@ static bool mlx5e_hw_gro_skb_has_enough_space(struct sk_buff *skb, > int nr_frags = skb_shinfo(skb)->nr_frags; > > if (page_size >= GRO_LEGACY_MAX_SIZE) > - return skb->len + data_bcnt <= GRO_LEGACY_MAX_SIZE; > + return skb->len + data_bcnt < GRO_LEGACY_MAX_SIZE; > else > - return page_size * nr_frags + data_bcnt <= GRO_LEGACY_MAX_SIZE; > + return skb_headlen(skb) + page_size * nr_frags + data_bcnt < > + GRO_LEGACY_MAX_SIZE; > } > > static void mlx5e_handle_rx_cqe_mpwrq_shampo(struct mlx5e_rq *rq, struct mlx5_cqe64 *cqe) > > base-commit: 51b093a7ba27476e1f639455f005e8d2e75390e4 The code looks good to me. Wait for Tariq's comments before re-spinning. Thanks, Dragos