linux-kernel - [PATCH net 3/5] net/mlx5e: Fix maxrate wraparound in threshold between units

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Message-ID: <1762681073-1084058-4-git-send-email-tariqt@nvidia.com>
Date: Sun, 9 Nov 2025 11:37:51 +0200
From: Tariq Toukan <tariqt@...dia.com>
To: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>, "David
 S. Miller" <davem@...emloft.net>
CC: Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
	Tariq Toukan <tariqt@...dia.com>, Mark Bloch <mbloch@...dia.com>,
	<netdev@...r.kernel.org>, <linux-rdma@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Gal Pressman <gal@...dia.com>
Subject: [PATCH net 3/5] net/mlx5e: Fix maxrate wraparound in threshold between units

From: Gal Pressman <gal@...dia.com>

The previous calculation used roundup() which caused an overflow for
rates between 25.5Gbps and 26Gbps.
For example, a rate of 25.6Gbps would result in using 100Mbps units with
value of 256, which would overflow the 8 bits field.

Simplify the upper_limit_mbps calculation by removing the
unnecessary roundup, and adjust the comparison to use <= to correctly
handle the boundary condition.

Fixes: d8880795dabf ("net/mlx5e: Implement DCBNL IEEE max rate")
Signed-off-by: Gal Pressman <gal@...dia.com>
Reviewed-by: Nimrod Oren <noren@...dia.com>
Signed-off-by: Tariq Toukan <tariqt@...dia.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_dcbnl.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_dcbnl.c b/drivers/net/ethernet/mellanox/mlx5/core/en_dcbnl.c
index d166c0d5189e..345614471052 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_dcbnl.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_dcbnl.c
@@ -595,18 +595,19 @@ static int mlx5e_dcbnl_ieee_setmaxrate(struct net_device *netdev,
 	struct mlx5_core_dev *mdev = priv->mdev;
 	u8 max_bw_value[IEEE_8021QAZ_MAX_TCS];
 	u8 max_bw_unit[IEEE_8021QAZ_MAX_TCS];
-	__u64 upper_limit_mbps = roundup(255 * MLX5E_100MB, MLX5E_1GB);
+	__u64 upper_limit_mbps;
 	int i;
 
 	memset(max_bw_value, 0, sizeof(max_bw_value));
 	memset(max_bw_unit, 0, sizeof(max_bw_unit));
+	upper_limit_mbps = 255 * MLX5E_100MB;
 
 	for (i = 0; i <= mlx5_max_tc(mdev); i++) {
 		if (!maxrate->tc_maxrate[i]) {
 			max_bw_unit[i]  = MLX5_BW_NO_LIMIT;
 			continue;
 		}
-		if (maxrate->tc_maxrate[i] < upper_limit_mbps) {
+		if (maxrate->tc_maxrate[i] <= upper_limit_mbps) {
 			max_bw_value[i] = div_u64(maxrate->tc_maxrate[i],
 						  MLX5E_100MB);
 			max_bw_value[i] = max_bw_value[i] ? max_bw_value[i] : 1;
-- 
2.31.1