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

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Message-ID: <d613c5a6-5081-4760-8a86-db1107bdc207@quicinc.com>
Date: Mon, 6 May 2024 13:50:48 -0700
From: "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>
To: 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>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Daniel Borkmann <daniel@...earbox.net>, bpf <bpf@...r.kernel.org>
CC: <kernel@...cinc.com>
Subject: Re: [RFC PATCH bpf-next v6 3/3] selftests/bpf: Handle forwarding of
 UDP CLOCK_TAI packets



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 -   

"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;",
>>  	},