From: Jakub Kicinski <kuba@kernel.org>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Jisheng Zhang <jszhang@kernel.org>,
Maxime Chevallier <maxime.chevallier@bootlin.com>,
Andrew Lunn <andrew+netdev@lunn.ch>,
"David S . Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>,
Maxime Coquelin <mcoquelin.stm32@gmail.com>,
Alexandre Torgue <alexandre.torgue@foss.st.com>,
netdev@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] net: stmmac: Disable checksum insertion for XDP frame TX
Date: Mon, 5 Oct 2026 16:28:29 -0700 [thread overview]
Message-ID: <20261005162829.74778c7d@kernel.org> (raw)
In-Reply-To: <f0d8c25f-96e1-4da8-af6c-3286610338ba@lunn.ch>
On Tue, 29 Sep 2026 22:29:14 +0200 Andrew Lunn wrote:
> On Tue, Sep 29, 2026 at 08:10:25PM +0800, Jisheng Zhang wrote:
> > stmmac enables TX checksum insertion for XDP frames whenever the queue
> > supports it. XDP frames carry no TX checksum offload request, so this
> > can overwrite a checksum already present in the packet.
> >
> > Pass false to stmmac_prepare_tx_desc() when transmitting an XDP frame
> > so that the packet is sent with its checksum fields unchanged.
>
> This seems odd to me.
>
> If the frame contains a checksum, it is either correct, and the
> hardware calculated one will come out the same, not an issue. Or the
> checksum in the frame is actually wrong, because the frame has got
> mangled by eBPF before sending it out, and you want the hardware to
> calculate the correct value.
>
> What an i missing?
Oops, missed this before applying. Fair, but also we shouldn't modify
the frame if user didn't ask for it. Perhaps 0 UDP csum is used, or
user is trying to build a testing tool and intentionally send bad csum.
I applied the patch to net-next. It can hurt as much as help, but the
direction seems right. At the very least any AF_XDP app expecting csum
insertion without asking for it would not be portable to other drivers.
next prev parent reply other threads:[~2026-10-05 23:28 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-29 12:10 Jisheng Zhang
2026-09-29 12:34 ` netdev-bot+sinfo
2026-09-29 20:29 ` Andrew Lunn
2026-10-05 23:28 ` Jakub Kicinski [this message]
2026-10-02 6:10 ` netdev-bot+sashiko
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