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Date: Wed, 29 Oct 2025 15:50:41 +0000
From: Simon Horman <horms@kernel.org>
To: Tariq Toukan <tariqt@nvidia.com>
Cc: Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>,
	Paolo Abeni <pabeni@redhat.com>,
	Andrew Lunn <andrew+netdev@lunn.ch>,
	"David S. Miller" <davem@davemloft.net>,
	Saeed Mahameed <saeedm@nvidia.com>,
	Leon Romanovsky <leon@kernel.org>, Mark Bloch <mbloch@nvidia.com>,
	netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
	linux-kernel@vger.kernel.org, Gal Pressman <gal@nvidia.com>,
	Dragos Tatulea <dtatulea@nvidia.com>
Subject: Re: [PATCH net 2/3] net/mlx5e: SHAMPO, Fix skb size check for 64K
 pages
Message-ID: <aQI30QptJw-xRGWQ@horms.kernel.org>
References: <1761634039-999515-1-git-send-email-tariqt@nvidia.com>
 <1761634039-999515-3-git-send-email-tariqt@nvidia.com>
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In-Reply-To: <1761634039-999515-3-git-send-email-tariqt@nvidia.com>

On Tue, Oct 28, 2025 at 08:47:18AM +0200, Tariq Toukan wrote:
> From: Dragos Tatulea <dtatulea@nvidia.com>
> 
> mlx5e_hw_gro_skb_has_enough_space() uses a formula to check if there is
> enough space in the skb frags to store more data. This formula is
> incorrect for 64K page sizes and it triggers early GRO session
> termination because the first fragment will blow up beyond
> GRO_LEGACY_MAX_SIZE.
> 
> This patch adds a special case for page sizes >= GRO_LEGACY_MAX_SIZE
> (64K) which will uses the skb->data_len instead. Within this context,
> this check will be safe from fragment overflow.

The above mentions skb->data_len, but the code uses skb->len.

Also, I think it would be worth describing why this is safe
in this context.

> 
> It is expected that the if statement will be optimized out as the
> check is done with constants.
> 
> Fixes: 92552d3abd32 ("net/mlx5e: HW_GRO cqe handler implementation")
> Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
> Signed-off-by: Tariq Toukan <tariqt@nvidia.com>

...