From: Andrew Lunn <andrew@lunn.ch>
To: Aldo Ariel <qwe.aldo@gmail.com>
Cc: wei.fang@nxp.com, frank.li@nxp.com, shenwei.wang@nxp.com,
imx@lists.linux.dev, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org, stable@vger.kernel.org,
Sashiko <sashiko-bot@kernel.org>
Subject: Re: [PATCH net v2] net: fec: reject oversized fragments before bounce-buffer memcpy
Date: Thu, 24 Sep 2026 14:40:50 +0200 [thread overview]
Message-ID: <a230cd62-db31-4128-acfa-93501d30aa39@lunn.ch> (raw)
In-Reply-To: <CAP48Hfto4qc285B3Jw7ZRuC-wGf57JOBPZOdrrAt-aDfGcas8Q@mail.gmail.com>
On Wed, Sep 23, 2026 at 06:22:01PM -0300, Aldo Ariel wrote:
> Hi Andrew,
>
> PKT_MAXBUF_SIZE = round_down(2048 - 64, 64) = 1984
> max_mtu (non-jumbo) = 1984 - VLAN_ETH_HLEN - ETH_FCS_LEN = 1962
>
> So for standard MTU, max_mtu < FEC_ENET_TX_FRSIZE and individual
> fragments should not exceed the bounce buffer.
>
> However, when the device supports jumbo frames,
> max_buf_size = MAX_JUMBO_BUF_SIZE (~16256) and max_mtu reaches ~16234.
> Scatter-gather fragments in that case can exceed FEC_ENET_TX_FRSIZE
> while still needing the bounce path for alignment or byte-swap.
>
> Should I respin with a check only for the jumbo path, or is the
> unconditional guard acceptable?
Can bounce buffers and jumbo be used at the same time?
How is the scatter-gather size determined? Maybe the better fix is to
set the fragment size based on the size of the bounce buffer when it
is in use?
Andrew
next prev parent reply other threads:[~2026-09-24 12:40 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-23 20:37 Aldo Ariel Panzardo
2026-09-23 21:00 ` Andrew Lunn
[not found] ` <CAP48Hfto4qc285B3Jw7ZRuC-wGf57JOBPZOdrrAt-aDfGcas8Q@mail.gmail.com>
2026-09-24 12:40 ` Andrew Lunn [this message]
2026-09-24 15:24 ` Shenwei Wang
2026-09-24 2:15 ` Wei Fang
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