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

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Date:   Wed, 15 Mar 2023 15:54:07 +0100
From:   Ilya Leoshkevich <iii@...ux.ibm.com>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     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, 2023-03-15 at 11:54 +0100, Alexander Lobakin 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;
>  
>         if (*payload == MARK_XMIT)

Okay, I'll take a look. Two quick observations for now:

- Unfortunately the above patch does not help.

- In dmesg I see:

    Driver unsupported XDP return value 0 on prog xdp_redirect (id 23)
    dev N/A, expect packet loss!