linux-kernel - Re: [PATCH iwl-next v7 5/9] igc: Add support for frame preemption verification

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Message-ID: <4882bd5b-1a64-4ac7-ba51-66143d029e8a@linux.intel.com>
Date: Wed, 5 Mar 2025 20:33:55 +0800
From: "Abdul Rahim, Faizal" <faizal.abdul.rahim@...ux.intel.com>
To: Vladimir Oltean <vladimir.oltean@....com>, ",chwee.lin.choong"@intel.com
Cc: Tony Nguyen <anthony.l.nguyen@...el.com>,
 Przemek Kitszel <przemyslaw.kitszel@...el.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S . Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Simon Horman <horms@...nel.org>, Russell King <linux@...linux.org.uk>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, Furong Xu <0x1207@...il.com>,
 Russell King <rmk+kernel@...linux.org.uk>,
 Serge Semin <fancer.lancer@...il.com>,
 Xiaolei Wang <xiaolei.wang@...driver.com>,
 Suraj Jaiswal <quic_jsuraj@...cinc.com>,
 Kory Maincent <kory.maincent@...tlin.com>, Gal Pressman <gal@...dia.com>,
 Jesper Nilsson <jesper.nilsson@...s.com>,
 Andrew Halaney <ahalaney@...hat.com>,
 Choong Yong Liang <yong.liang.choong@...ux.intel.com>,
 Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
 Vinicius Costa Gomes <vinicius.gomes@...el.com>,
 intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, bpf@...r.kernel.org
Subject: Re: [PATCH iwl-next v7 5/9] igc: Add support for frame preemption
 verification

On 4/3/2025 11:26 pm, Vladimir Oltean wrote:
> On Mon, Mar 03, 2025 at 05:26:54AM -0500, Faizal Rahim wrote:
>> +static inline bool igc_fpe_is_verify_or_response(union igc_adv_rx_desc *rx_desc,
>> +						 unsigned int size)
>> +{
>> +	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);
>> +
>> +	return (smd == IGC_RXD_STAT_SMD_TYPE_V || smd == IGC_RXD_STAT_SMD_TYPE_R) &&
>> +		size == SMD_FRAME_SIZE;
>> +}
> 
> The NIC should explicitly not respond to frames which have an SMD-V but
> are not "verify" mPackets (7 octets of 0x55 + 1 octet SMD-V + 60 octets
> of 0x00 + mCRC - as per 802.3 definitions). Similarly, it should only
> treat SMD-R frames which contain 7 octets of 0x55 + 1 octet SMD-R + 60
> octets of 0x00 + mCRC as "respond" mPackets, and only advance its
> verification state machine based on those.
> 
> Specifically, it doesn't look like you are ensuring the packet payload
> contains 60 octets of zeroes. Is this something that the hardware
> already does for you, or is it something that needs further validation
> and differentiation in software?

The hardware doesn’t handle this, so the igc driver have to do it manually. 
I missed this handling, and Chwee Lin also noticed the issue while testing 
this patch series—it wasn’t rejecting SMD-V and SMD-R with a non-zero 
payload. I’ll update this patch to include the fix that Chwee Lin 
implemented and tested. Thanks.