[PATCH] app/test-pmd: fix L4 checksum with padding data

[Ferruh Yigit]

On 11/3/2023 2:49 AM, Deng, KaiwenX wrote:
> 
> 
>> -----Original Message-----
>> From: Ferruh Yigit <ferruh.yigit at amd.com>
>> Sent: Friday, November 3, 2023 3:20 AM
>> To: Deng, KaiwenX <kaiwenx.deng at intel.com>; dev at dpdk.org
>> Cc: stable at dpdk.org; Yang, Qiming <qiming.yang at intel.com>; Zhou, YidingX
>> <yidingx.zhou at intel.com>; Singh, Aman Deep <aman.deep.singh at intel.com>;
>> Zhang, Yuying <yuying.zhang at intel.com>; Matz, Olivier
>> <olivier.matz at 6wind.com>; De Lara Guarch, Pablo
>> <pablo.de.lara.guarch at intel.com>
>> Subject: Re: [PATCH] app/test-pmd: fix L4 checksum with padding data
>>
>> On 8/4/2023 9:28 AM, Kaiwen Deng wrote:
>>> IEEE 802 packets may have a minimum size limit. The data fields should
>>> be padded when necessary. In some cases, the padding data is not zero.
>>> Testpmd does not trim these IP packets to the true length of the
>>> frame, so errors will occur when calculating TCP or UDP checksum.
>>>
>>
>> Hi Kaiwen,
>>
>> I am trying to understand the problem, what is the testcase that has checksum
>> error?
>>
>> Are the received mbuf data_len & pkt_len wrong? Instead of trying to fix the
>> mbuf during forwarding, can we fix where packet generated?
>>
> Hi Ferruh,
> 
> In effect, the packet is padded by the switch. 
> IEEE 802 packets may have a minimum size limit. The data fields should 
> be padded by switch when necessary. In some switches, the padding data is not zero. 
> 
> Csumonly doesn't trim these packets to the true length of the frame. 
> In csumonly, the received mbuf data_len is the true length of the packet plus the padding data len.
> Therefore, padding data is included in the checksum calculation.
> When the padding data is not zero, the checksum is wrong.
> 

Thanks for clarification.

Even some non-zero padding added, it will calculate the csum
successfully, but I assume in this case csum becomes different than
expected csum and test fails?

In this case why not fix the generated packets, and make them compatible
to minimum size requirement? What is generating packets?


>>> This commit fixes this issue by triming IP packets to the true length
>>> of the frame in testpmd.
>>>
>>> Fixes: 03d17e4d0179 ("app/testpmd: do not change IP addrs in checksum
>>> engine")
>>> Cc: stable at dpdk.org
>>>
>>> Signed-off-by: Kaiwen Deng <kaiwenx.deng at intel.com>
>>> ---
>>>  app/test-pmd/csumonly.c | 32 ++++++++++++++++++++++++++++++++
>>>  1 file changed, 32 insertions(+)
>>>
>>> diff --git a/app/test-pmd/csumonly.c b/app/test-pmd/csumonly.c index
>>> 7af635e3f7..58b72b714a 100644
>>> --- a/app/test-pmd/csumonly.c
>>> +++ b/app/test-pmd/csumonly.c
>>> @@ -853,12 +853,14 @@ pkt_burst_checksum_forward(struct
>> fwd_stream *fs)
>>>  	uint16_t nb_rx;
>>>  	uint16_t nb_prep;
>>>  	uint16_t i;
>>> +	uint16_t pad_len;
>>>  	uint64_t rx_ol_flags, tx_ol_flags;
>>>  	uint64_t tx_offloads;
>>>  	uint32_t rx_bad_ip_csum;
>>>  	uint32_t rx_bad_l4_csum;
>>>  	uint32_t rx_bad_outer_l4_csum;
>>>  	uint32_t rx_bad_outer_ip_csum;
>>> +	uint32_t l3_off;
>>>  	struct testpmd_offload_info info;
>>>
>>>  	/* receive a burst of packet */
>>> @@ -980,6 +982,36 @@ pkt_burst_checksum_forward(struct fwd_stream
>> *fs)
>>>  			l3_hdr = (char *)l3_hdr + info.outer_l3_len +
>> info.l2_len;
>>>  		}
>>>
>>> +		if (info.is_tunnel) {
>>> +			l3_off = info.outer_l2_len +
>>> +					info.outer_l3_len +
>>> +					info.l2_len;
>>> +		} else {
>>> +			l3_off = info.l2_len;
>>> +		}
>>> +		switch (info.ethertype) {
>>> +		case _htons(RTE_ETHER_TYPE_IPV4):
>>> +			pad_len = rte_pktmbuf_data_len(m) -
>>> +					(l3_off +
>>> +					rte_be_to_cpu_16(
>>> +					((struct rte_ipv4_hdr *)l3_hdr)-
>>> total_length));
>>> +			break;
>>> +		case _htons(RTE_ETHER_TYPE_IPV6):
>>> +			pad_len = rte_pktmbuf_data_len(m) -
>>> +					(l3_off +
>>> +					rte_be_to_cpu_16(
>>> +					((struct rte_ipv6_hdr *)l3_hdr)-
>>> payload_len));
>>> +			break;
>>> +		default:
>>> +			pad_len = 0;
>>> +			break;
>>> +		}
>>> +
>>> +		if (pad_len) {
>>> +			rte_pktmbuf_data_len(m) =
>> rte_pktmbuf_data_len(m) - pad_len;
>>> +			rte_pktmbuf_pkt_len(m) = rte_pktmbuf_data_len(m);
>>> +		}
>>> +
>>>  		/* step 2: depending on user command line configuration,
>>>  		 * recompute checksum either in software or flag the
>>>  		 * mbuf to offload the calculation to the NIC. If TSO
>