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

[Simon Horman <horms@kernel.org>]

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@siemens.com>

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