netdev - Re: [PATCH net 1/3] net: fec: dynamically set the NETDEV_XDP_ACT_NDO

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Message-ID: <87mt0bb5cm.fsf@toke.dk>
Date: Wed, 05 Jul 2023 01:54:17 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Andrew Lunn <andrew@...n.ch>, wei.fang@....com
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, ast@...nel.org, daniel@...earbox.net, hawk@...nel.org,
 john.fastabend@...il.com, shenwei.wang@....com, xiaoning.wang@....com,
 netdev@...r.kernel.org, linux-imx@....com, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org
Subject: Re: [PATCH net 1/3] net: fec: dynamically set the
 NETDEV_XDP_ACT_NDO_XMIT feature of XDP

Andrew Lunn <andrew@...n.ch> writes:

> On Tue, Jul 04, 2023 at 04:29:14PM +0800, wei.fang@....com wrote:
>> From: Wei Fang <wei.fang@....com>
>> 
>> When a XDP program is installed or uninstalled, fec_restart() will
>> be invoked to reset MAC and buffer descriptor rings. It's reasonable
>> not to transmit any packet during the process of reset. However, the
>> NETDEV_XDP_ACT_NDO_XMIT bit of xdp_features is enabled by default,
>> that is to say, it's possible that the fec_enet_xdp_xmit() will be
>> invoked even if the process of reset is not finished. In this case,
>> the redirected XDP frames might be dropped and available transmit BDs
>> may be incorrectly deemed insufficient. So this patch disable the
>> NETDEV_XDP_ACT_NDO_XMIT feature by default and dynamically configure
>> this feature when the bpf program is installed or uninstalled.
>
> I don't know much about XDP, so please excuse what might be a stupid
> question.
>
> Is this a generic issue? Should this
> xdp_features_clear_redirect_target(dev) /
> xdp_features_set_redirect_target(dev, false) be done in the core?

No, because not all drivers require an XDP program to be attached to
support being a redirect target (which is one of the reasons we
introduced these feature bits in the first place :)).

-Toke