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Message-ID: <6db57eb4-02c2-9443-b9eb-21c499142c98@intel.com>
Date: Thu, 9 Feb 2023 21:04:31 +0100
From: Alexander Lobakin <alexandr.lobakin@...el.com>
To: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>
CC: Toke Høiland-Jørgensen <toke@...hat.com>,
"Martin KaFai Lau" <martin.lau@...ux.dev>,
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>
Subject: Re: [PATCH bpf] bpf, test_run: fix &xdp_frame misplacement for
LIVE_FRAMES
From: Alexander Lobakin <alexandr.lobakin@...el.com>
Date: Thu, 9 Feb 2023 18:28:27 +0100
> &xdp_buff and &xdp_frame are bound in a way that
>
> xdp_buff->data_hard_start == xdp_frame
[...]
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index 2723623429ac..c3cce7a8d47d 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -97,8 +97,11 @@ static bool bpf_test_timer_continue(struct bpf_test_timer *t, int iterations,
> struct xdp_page_head {
> struct xdp_buff orig_ctx;
> struct xdp_buff ctx;
> - struct xdp_frame frm;
> - u8 data[];
> + union {
> + /* ::data_hard_start starts here */
> + DECLARE_FLEX_ARRAY(struct xdp_frame, frm);
> + DECLARE_FLEX_ARRAY(u8, data);
> + };
BTW, xdp_frame here starts at 112 byte offset, i.e. in 16 bytes a
cacheline boundary is hit, so xdp_frame gets sliced into halves: 16
bytes in CL1 + 24 bytes in CL2. Maybe we'd better align this union to
%NET_SKB_PAD / %SMP_CACHE_BYTES / ... to avoid this?
(but in bpf-next probably)
> };
>
> struct xdp_test_data {
Thanks,
Olek
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