linux-kernel - Re: [PATCH bpf-next v3 0/4] xdp: recycle Page Pool backed skbs built from XDP frames

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Message-ID: <CAADnVQLRq7H_-L_agV1Dh9mkdvekZZt9inbbXYFdTRumcBy85g@mail.gmail.com>
Date:   Wed, 15 Mar 2023 09:55:07 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     Ilya Leoshkevich <iii@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Song Liu <song@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Menglong Dong <imagedong@...cent.com>,
        Mykola Lysenko <mykolal@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 0/4] xdp: recycle Page Pool backed skbs built
 from XDP frames

On Wed, Mar 15, 2023 at 3:55 AM Alexander Lobakin
<aleksander.lobakin@...el.com> wrote:
>
> From: Alexander Lobakin <aleksander.lobakin@...el.com>
> Date: Wed, 15 Mar 2023 10:56:25 +0100
>
> > From: Alexei Starovoitov <alexei.starovoitov@...il.com>
> > Date: Tue, 14 Mar 2023 16:54:25 -0700
> >
> >> On Tue, Mar 14, 2023 at 11:52 AM Alexei Starovoitov
> >> <alexei.starovoitov@...il.com> wrote:
> >
> > [...]
> >
> >> test_xdp_do_redirect:PASS:prog_run 0 nsec
> >> test_xdp_do_redirect:PASS:pkt_count_xdp 0 nsec
> >> test_xdp_do_redirect:PASS:pkt_count_zero 0 nsec
> >> test_xdp_do_redirect:FAIL:pkt_count_tc unexpected pkt_count_tc: actual
> >> 220 != expected 9998
> >> test_max_pkt_size:PASS:prog_run_max_size 0 nsec
> >> test_max_pkt_size:PASS:prog_run_too_big 0 nsec
> >> close_netns:PASS:setns 0 nsec
> >> #289 xdp_do_redirect:FAIL
> >> Summary: 270/1674 PASSED, 30 SKIPPED, 1 FAILED
> >>
> >> Alex,
> >> could you please take a look at why it's happening?
> >>
> >> I suspect it's an endianness issue in:
> >>         if (*metadata != 0x42)
> >>                 return XDP_ABORTED;
> >> but your patch didn't change that,
> >> so I'm not sure why it worked before.
> >
> > Sure, lemme fix it real quick.
>
> Hi Ilya,
>
> Do you have s390 testing setups? Maybe you could take a look, since I
> don't have one and can't debug it? Doesn't seem to be Endianness issue.
> I mean, I have this (the below patch), but not sure it will fix
> anything -- IIRC eBPF arch always matches the host arch ._.
> I can't figure out from the code what does happen wrongly :s And it
> happens only on s390.
>
> Thanks,
> Olek
> ---
> diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c b/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c
> index 662b6c6c5ed7..b21371668447 100644
> --- a/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c
> +++ b/tools/testing/selftests/bpf/prog_tests/xdp_do_redirect.c
> @@ -107,7 +107,7 @@ void test_xdp_do_redirect(void)
>                             .attach_point = BPF_TC_INGRESS);
>
>         memcpy(&data[sizeof(__u32)], &pkt_udp, sizeof(pkt_udp));
> -       *((__u32 *)data) = 0x42; /* metadata test value */
> +       *((__u32 *)data) = htonl(0x42); /* metadata test value */
>
>         skel = test_xdp_do_redirect__open();
>         if (!ASSERT_OK_PTR(skel, "skel"))
> diff --git a/tools/testing/selftests/bpf/progs/test_xdp_do_redirect.c b/tools/testing/selftests/bpf/progs/test_xdp_do_redirect.c
> index cd2d4e3258b8..2475bc30ced2 100644
> --- a/tools/testing/selftests/bpf/progs/test_xdp_do_redirect.c
> +++ b/tools/testing/selftests/bpf/progs/test_xdp_do_redirect.c
> @@ -1,5 +1,6 @@
>  // SPDX-License-Identifier: GPL-2.0
>  #include <vmlinux.h>
> +#include <bpf/bpf_endian.h>
>  #include <bpf/bpf_helpers.h>
>
>  #define ETH_ALEN 6
> @@ -28,7 +29,7 @@ volatile int retcode = XDP_REDIRECT;
>  SEC("xdp")
>  int xdp_redirect(struct xdp_md *xdp)
>  {
> -       __u32 *metadata = (void *)(long)xdp->data_meta;
> +       __be32 *metadata = (void *)(long)xdp->data_meta;
>         void *data_end = (void *)(long)xdp->data_end;
>         void *data = (void *)(long)xdp->data;
>
> @@ -44,7 +45,7 @@ int xdp_redirect(struct xdp_md *xdp)
>         if (metadata + 1 > data)
>                 return XDP_ABORTED;
>
> -       if (*metadata != 0x42)
> +       if (*metadata != __bpf_htonl(0x42))
>                 return XDP_ABORTED;

Looks sane to me.
I'd probably use 'u8 * metadata' instead. Both in bpf and user space
just not to worry about endianness.
Could you please submit an official patch and let CI judge?