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

Abdul Rahim, Faizal
2025-03-07T11:54:38Z

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.