linux-kernel - Re: [PATCH bpf-next v4] bpf, test_run: fix &xdp_frame misplacement for LIVE

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Date:   Fri, 17 Feb 2023 12:32:36 -0800
From:   Martin KaFai Lau <martin.lau@...ux.dev>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Song Liu <song@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH bpf-next v4] bpf, test_run: fix &xdp_frame misplacement
 for LIVE_FRAMES

On 2/15/23 10:54 AM, Alexander Lobakin wrote:
> +#if BITS_PER_LONG == 64 && PAGE_SIZE == SZ_4K
> +/* tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c:%MAX_PKT_SIZE
> + * must be updated accordingly when any of these changes, otherwise BPF
> + * selftests will fail.
> + */
> +#ifdef __s390x__
> +#define TEST_MAX_PKT_SIZE 3216
> +#else
> +#define TEST_MAX_PKT_SIZE 3408

I have to revert this patch for now. It is not right to assume cache line size:
https://lore.kernel.org/bpf/50c35055-afa9-d01e-9a05-ea5351280e4f@intel.com/

Please resubmit and consider if this static_assert is really needed in the 
kernel test_run.c.

> +#endif
> +static_assert(SKB_WITH_OVERHEAD(TEST_XDP_FRAME_SIZE - XDP_PACKET_HEADROOM) ==
> +	      TEST_MAX_PKT_SIZE);
> +#endif