linux-kernel - Re: [RFC PATCH bpf-next v6 3/3] selftests/bpf: Handle forwarding of UDP CLOCK

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Date: Mon, 6 May 2024 17:54:13 -0700
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Andrew Halaney <ahalaney@...hat.com>,
 Martin KaFai Lau <martin.lau@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, bpf <bpf@...r.kernel.org>,
 kernel@...cinc.com
Subject: Re: [RFC PATCH bpf-next v6 3/3] selftests/bpf: Handle forwarding of
 UDP CLOCK_TAI packets

On 5/6/24 1:50 PM, Abhishek Chauhan (ABC) wrote:
> 
> 
> On 5/6/2024 12:04 PM, Willem de Bruijn wrote:
>> Abhishek Chauhan wrote:
>>> With changes in the design to forward CLOCK_TAI in the skbuff
>>> framework,  existing selftest framework needs modification
>>> to handle forwarding of UDP packets with CLOCK_TAI as clockid.
>>>
>>> Link: https://lore.kernel.org/netdev/bc037db4-58bb-4861-ac31-a361a93841d3@linux.dev/
>>> Signed-off-by: Abhishek Chauhan <quic_abchauha@...cinc.com>
>>> ---
>>>   tools/include/uapi/linux/bpf.h                | 15 ++++---
>>>   .../selftests/bpf/prog_tests/ctx_rewrite.c    | 10 +++--
>>>   .../selftests/bpf/prog_tests/tc_redirect.c    |  3 --
>>>   .../selftests/bpf/progs/test_tc_dtime.c       | 39 +++++++++----------
>>>   4 files changed, 34 insertions(+), 33 deletions(-)
>>>
>>> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
>>> index 90706a47f6ff..25ea393cf084 100644
>>> --- a/tools/include/uapi/linux/bpf.h
>>> +++ b/tools/include/uapi/linux/bpf.h
>>> @@ -6207,12 +6207,17 @@ union {					\
>>>   	__u64 :64;			\
>>>   } __attribute__((aligned(8)))
>>>   
>>> +/* The enum used in skb->tstamp_type. It specifies the clock type
>>> + * of the time stored in the skb->tstamp.
>>> + */
>>>   enum {
>>> -	BPF_SKB_TSTAMP_UNSPEC,
>>> -	BPF_SKB_TSTAMP_DELIVERY_MONO,	/* tstamp has mono delivery time */
>>> -	/* For any BPF_SKB_TSTAMP_* that the bpf prog cannot handle,
>>> -	 * the bpf prog should handle it like BPF_SKB_TSTAMP_UNSPEC
>>> -	 * and try to deduce it by ingress, egress or skb->sk->sk_clockid.
>>> +	BPF_SKB_TSTAMP_UNSPEC = 0,		/* DEPRECATED */
>>> +	BPF_SKB_TSTAMP_DELIVERY_MONO = 1,	/* DEPRECATED */
>>> +	BPF_SKB_CLOCK_REALTIME = 0,
>>> +	BPF_SKB_CLOCK_MONOTONIC = 1,
>>> +	BPF_SKB_CLOCK_TAI = 2,
>>> +	/* For any future BPF_SKB_CLOCK_* that the bpf prog cannot handle,
>>> +	 * the bpf prog can try to deduce it by ingress/egress/skb->sk->sk_clockid.
>>>   	 */
>>>   };
>>>   
>>> diff --git a/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c b/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
>>> index 3b7c57fe55a5..71940f4ef0fb 100644
>>> --- a/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
>>> +++ b/tools/testing/selftests/bpf/prog_tests/ctx_rewrite.c
>>> @@ -69,15 +69,17 @@ static struct test_case test_cases[] = {
>>>   	{
>>>   		N(SCHED_CLS, struct __sk_buff, tstamp),
>>>   		.read  = "r11 = *(u8 *)($ctx + sk_buff::__mono_tc_offset);"
>>> -			 "w11 &= 3;"
>>> -			 "if w11 != 0x3 goto pc+2;"
>>> +			 "if w11 == 0x4 goto pc+1;"
>>> +			 "goto pc+4;"
>>> +			 "if w11 == 0x3 goto pc+1;"
>>> +			 "goto pc+2;"
>>
>> Not an expert on this code, and I see that the existing code already
>> has this below, but: isn't it odd and unnecessary to jump to an
>> unconditional jump statement?
>>
> I am closely looking into your comment and i will evalute it(Martin can correct me
> if the jumps are correct or not as i am new to BPF as well) but i found out that
> JSET = "&" and not "==". So the above two ins has to change from -

Yes, this should be bitwise "&" instead of "==".

The bpf CI did report this: 
https://github.com/kernel-patches/bpf/actions/runs/8947652196/job/24579927178

Please monitor the bpf CI test result.

Do you have issue running the test locally?

> 
> "if w11 == 0x4 goto pc+1;" ==>(needs to be corrected to) "if w11 & 0x4 goto pc+1;"
>   "if w11 == 0x3 goto pc+1;" ==> (needs to be correct to) "if w11 & 0x3 goto pc+1;"
> 
> 
>>>   			 "$dst = 0;"
>>>   			 "goto pc+1;"
>>>   			 "$dst = *(u64 *)($ctx + sk_buff::tstamp);",
>>>   		.write = "r11 = *(u8 *)($ctx + sk_buff::__mono_tc_offset);"
>>> -			 "if w11 & 0x2 goto pc+1;"
>>> +			 "if w11 & 0x4 goto pc+1;"
>>>   			 "goto pc+2;"
>>> -			 "w11 &= -2;"
>>> +			 "w11 &= -3;"
> Martin,
> Also i am not sure why the the dissembly complains because the value of SKB_TSTAMP_TYPE_MASK = 3 and we are
> negating it ~3 = -3.
> 
>    Can't match disassembly(left) with pattern(right):
>    r11 = *(u8 *)(r1 +129)  ;  r11 = *(u8 *)($ctx + sk_buff::__mono_tc_offset)
>    if w11 & 0x4 goto pc+1  ;  if w11 & 0x4 goto pc+1
>    goto pc+2               ;  goto pc+2
>    w11 &= -4               ;  w11 &= -3
> 
>>>   			 "*(u8 *)($ctx + sk_buff::__mono_tc_offset) = r11;"
>>>   			 "*(u64 *)($ctx + sk_buff::tstamp) = $src;",
>>>   	},