From: Simon Horman <simon.horman@corigine.com>
To: Vladimir Oltean <vladimir.oltean@nxp.com>
Cc: netdev@vger.kernel.org, Andrew Lunn <andrew@lunn.ch>,
Florian Fainelli <f.fainelli@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Claudiu Manoil <claudiu.manoil@nxp.com>,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
UNGLinuxDriver@microchip.com,
Xiaoliang Yang <xiaoliang.yang_1@nxp.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] net: dsa: felix: fix taprio guard band overflow at 10Mbps with jumbo frames
Date: Wed, 14 Jun 2023 14:05:15 +0200 [thread overview]
Message-ID: <ZIms+0/KDpU9dd3y@corigine.com> (raw)
In-Reply-To: <20230613170907.2413559-1-vladimir.oltean@nxp.com>
On Tue, Jun 13, 2023 at 08:09:07PM +0300, Vladimir Oltean wrote:
> The DEV_MAC_MAXLEN_CFG register contains a 16-bit value - up to 65535.
> Plus 2 * VLAN_HLEN (4), that is up to 65543.
>
> The picos_per_byte variable is the largest when "speed" is lowest -
> SPEED_10 = 10. In that case it is (1000000L * 8) / 10 = 800000.
>
> Their product - 52434400000 - exceeds 32 bits, which is a problem,
> because apparently, a multiplication between two 32-bit factors is
> evaluated as 32-bit before being assigned to a 64-bit variable.
> In fact it's a problem for any MTU value larger than 5368.
>
> Cast one of the factors of the multiplication to u64 to force the
> multiplication to take place on 64 bits.
>
> Issue found by Coverity.
>
> Fixes: 55a515b1f5a9 ("net: dsa: felix: drop oversized frames with tc-taprio instead of hanging the port")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
In a similar vein, you may want to consider the following suggestion from
Coccinelle.
.../felix_vsc9959.c:1382:2-8: WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead.
next prev parent reply other threads:[~2023-06-14 12:05 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-13 17:09 [PATCH net] net: dsa: felix: fix taprio guard band overflow at 10Mbps with jumbo frames Vladimir Oltean
2023-06-14 12:05 ` Simon Horman [this message]
2023-06-14 12:17 ` Vladimir Oltean
2023-06-14 13:15 ` Simon Horman
2023-06-15 6:10 ` patchwork-bot+netdevbpf
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