Re: [PATCH net-net] tun: Assign missing bpf_net_context.
From: Jakub Kicinski
Date: Wed Jul 03 2024 - 15:01:59 EST
On Wed, 3 Jul 2024 14:27:58 +0200 Sebastian Andrzej Siewior wrote:
> During the introduction of struct bpf_net_context handling for
> XDP-redirect, the tun driver has been missed.
>
> Set the bpf_net_context before invoking BPF XDP program within the TUN
> driver.
Sorry if I'm missing the point but I think this is insufficient.
You've covered the NAPI-like entry point to the Rx stack in your
initial work, but there's also netif_receive_skb() which drivers
may call outside of NAPI, simply disabling BH before the call.
The only concern in that case is that we end up in do_xdp_generic(),
and there's no bpf_net_set_ctx() anywhere on the way. So my intuition
would be to add the bpf_net_set_ctx() inside the if(xdp_prog) in
do_xdp_generic(). "XDP generic" has less stringent (more TC-like)
perf requirements, so setting context once per packet should be fine.
And it will also cover drivers like TUN which use both
netif_receive_skb() and call do_xdp_generic(), in a single place.