Re: [PATCH iwl-next v8 07/11] igc: add support for frame preemption verification

["Abdul Rahim, Faizal" <faizal.abdul.rahim@linux.intel.com>]

On 6/3/2025 8:28 am, Vladimir Oltean wrote:
> On Wed, Mar 05, 2025 at 08:00:22AM -0500, Faizal Rahim wrote:
>> Co-developed-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
>> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
>> Co-developed-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
>> Signed-off-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
>> Co-developed-by: Chwee-Lin Choong <chwee.lin.choong@intel.com>
>> Signed-off-by: Chwee-Lin Choong <chwee.lin.choong@intel.com>
>> Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
>> ---
>> +
>> +static inline bool igc_fpe_is_verify_or_response(union igc_adv_rx_desc *rx_desc,
>> +						 unsigned int size, void *pktbuf)
>> +{
>> +	u32 status_error = le32_to_cpu(rx_desc->wb.upper.status_error);
>> +	static const u8 zero_payload[SMD_FRAME_SIZE] = {0};
>> +	int smd;
>> +
>> +	smd = FIELD_GET(IGC_RXDADV_STAT_SMD_TYPE_MASK, status_error);
>> +
>> +	return (smd == IGC_RXD_STAT_SMD_TYPE_V || smd == IGC_RXD_STAT_SMD_TYPE_R) &&
>> +		size == SMD_FRAME_SIZE &&
>> +		!memcmp(pktbuf, zero_payload, SMD_FRAME_SIZE); /* Buffer is all zeros */
> 
> Using this definition...
> 
>> +}
>> +
>> +static inline void igc_fpe_lp_event_status(union igc_adv_rx_desc *rx_desc,
>> +					   struct ethtool_mmsv *mmsv)
>> +{
>> +	u32 status_error = le32_to_cpu(rx_desc->wb.upper.status_error);
>> +	int smd;
>> +
>> +	smd = FIELD_GET(IGC_RXDADV_STAT_SMD_TYPE_MASK, status_error);
>> +
>> +	if (smd == IGC_RXD_STAT_SMD_TYPE_V)
>> +		ethtool_mmsv_event_handle(mmsv, ETHTOOL_MMSV_LP_SENT_VERIFY_MPACKET);
>> +	else if (smd == IGC_RXD_STAT_SMD_TYPE_R)
>> +		ethtool_mmsv_event_handle(mmsv, ETHTOOL_MMSV_LP_SENT_RESPONSE_MPACKET);
>> +}
>> @@ -2617,6 +2617,15 @@ static int igc_clean_rx_irq(struct igc_q_vector *q_vector, const int budget)
>>   			size -= IGC_TS_HDR_LEN;
>>   		}
>>   
>> +		if (igc_fpe_is_pmac_enabled(adapter) &&
>> +		    igc_fpe_is_verify_or_response(rx_desc, size, pktbuf)) {
> 
> ... invalid SMD-R and SMD-V frames will skip this code block altogether, and
> will be passed up the network stack, and visible at least in tcpdump, correct?
> Essentially, if the link partner would craft an ICMP request packet with
> an SMD-V or SMD-R, your station would respond to it, which is incorrect.
> 
> A bit strange, the behavior in this case seems a bit under-specified in
> the standard, and I don't see any counter that should be incremented.
> 
>> +			igc_fpe_lp_event_status(rx_desc, &adapter->fpe.mmsv);
>> +			/* Advance the ring next-to-clean */
>> +			igc_is_non_eop(rx_ring, rx_desc);
>> +			cleaned_count++;
>> +			continue;
>> +		}
> 
> To fix this, don't you want to merge the unnaturally split
> igc_fpe_is_verify_or_response() and igc_fpe_lp_event_status() into a
> single function, which returns true whenever the mPacket should be
> consumed by the driver, but decides whether to emit a mmsv event on its
> own? Merging the two would also avoid reading rx_desc->wb.upper.status_error
> twice.
> 
> Something like this:
> 
> static inline bool igc_fpe_handle_mpacket(struct igc_adapter *adapter,
> 					  union igc_adv_rx_desc *rx_desc,
> 					  unsigned int size, void *pktbuf)
> {
> 	u32 status_error = le32_to_cpu(rx_desc->wb.upper.status_error);
> 	int smd;
> 
> 	smd = FIELD_GET(IGC_RXDADV_STAT_SMD_TYPE_MASK, status_error);
> 	if (smd != IGC_RXD_STAT_SMD_TYPE_V && smd != IGC_RXD_STAT_SMD_TYPE_R)
> 		return false;
> 
> 	if (size == SMD_FRAME_SIZE && mem_is_zero(pktbuf, SMD_FRAME_SIZE)) {
> 		struct ethtool_mmsv *mmsv = &adapter->fpe.mmsv;
> 		enum ethtool_mmsv_event event;
> 
> 		if (smd == IGC_RXD_STAT_SMD_TYPE_V)
> 			event = ETHTOOL_MMSV_LP_SENT_VERIFY_MPACKET;
> 		else
> 			event = ETHTOOL_MMSV_LP_SENT_RESPONSE_MPACKET;
> 
> 		ethtool_mmsv_event_handle(mmsv, event);
> 	}
> 
> 	return true;
> }
> 
> 		if (igc_fpe_is_pmac_enabled(adapter) &&
> 		    igc_fpe_handle_mpacket(adapter, rx_desc, size, pktbuf)) {
> 			/* Advance the ring next-to-clean */
> 			igc_is_non_eop(rx_ring, rx_desc);
> 			cleaned_count++;
> 			continue;
> 		}
> 
> [ also remark the use of mem_is_zero() instead of memcmp() with a buffer
>    pre-filled with zeroes. It should be more efficient, for the simple
>    reason that it's accessing a single memory buffer and not two. Though
>    I'm surprised how widespread the memcmp() pattern is throughout the
>    kernel. ]

Thanks for the suggestion—it reads much better and flows smoothly. Got it 
on the driver needing to consume a non-zero packet buffer from SMD-V and SMD-R.