netdev - Re: [PATCH] igc: Fix HW RX timestamp when passed by ZC XDP

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Message-ID: <20250131100545.GF24105@kernel.org>
Date: Fri, 31 Jan 2025 10:05:45 +0000
From: Simon Horman <horms@...nel.org>
To: Zdenek Bouska <zdenek.bouska@...mens.com>
Cc: Tony Nguyen <anthony.l.nguyen@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Vinicius Costa Gomes <vinicius.gomes@...el.com>,
	Florian Bezdeka <florian.bezdeka@...mens.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Song Yoong Siang <yoong.siang.song@...el.com>,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH] igc: Fix HW RX timestamp when passed by ZC XDP

On Tue, Jan 28, 2025 at 01:26:48PM +0100, Zdenek Bouska wrote:
> Fixes HW RX timestamp in the following scenario:
> - AF_PACKET socket with enabled HW RX timestamps is created
> - AF_XDP socket with enabled zero copy is created
> - frame is forwarded to the BPF program, where the timestamp should
>   still be readable (extracted by igc_xdp_rx_timestamp(), kfunc
>   behind bpf_xdp_metadata_rx_timestamp())
> - the frame got XDP_PASS from BPF program, redirecting to the stack
> - AF_PACKET socket receives the frame with HW RX timestamp
> 
> Moves the skb timestamp setting from igc_dispatch_skb_zc() to
> igc_construct_skb_zc() so that igc_construct_skb_zc() is similar to
> igc_construct_skb().
> 
> This issue can also be reproduced by running:
>  # tools/testing/selftests/bpf/xdp_hw_metadata enp1s0
> When a frame with the wrong port 9092 (instead of 9091) is used:
>  # echo -n xdp | nc -u -q1 192.168.10.9 9092
> then the RX timestamp is missing and xdp_hw_metadata prints:
>  skb hwtstamp is not found!
> 
> With this fix or when copy mode is used:
>  # tools/testing/selftests/bpf/xdp_hw_metadata -c enp1s0
> then RX timestamp is found and xdp_hw_metadata prints:
>  found skb hwtstamp = 1736509937.852786132
> 
> Fixes: 069b142f5819 ("igc: Add support for PTP .getcyclesx64()")
> Signed-off-by: Zdenek Bouska <zdenek.bouska@...mens.com>

Reviewed-by: Simon Horman <horms@...nel.org>