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 11:54:11 +0100
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Alexander Lobakin <aleksander.lobakin@...el.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

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)