Re: [PATCH v4] net/hns3: fix Rx packet without CRC data

[Stephen Hemminger <stephen@networkplumber.org>]

On Wed, 27 Nov 2024 18:08:07 +0800
Jie Hai <haijie1@huawei.com> wrote:

> From: Dengdui Huang <huangdengdui@huawei.com>
> 
> When KEEP_CRC offload is enabled, the CRC data is still stripped
> in following cases:
> 1. For HIP08 network engine, the packet type is TCP and the length
>    is less than or equal to 60B.
> 2. For HIP09 network engine, the packet type is IP and the length
>    is less than or equal to 60B.
> 
> So driver has to recaculate packet CRC for this rare scenarios.
> 
> In addition, to avoid impacting performance, KEEP_CRC is not
> supported when NEON or SVE algorithm is used.
> 
> Fixes: 8973d7c4ca12 ("net/hns3: support keeping CRC")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Dengdui Huang <huangdengdui@huawei.com>
> Acked-by: Huisong Li <lihuisong@huawei.com>
> Acked-by: Jie Hai <haijie1@huawei.com>
> ---

There is another issue around CRC in this driver.
If keep crc is enabled and the packet is received into a multisegment mbuf
and the CRC bytes are the only data left in the last segment
then the driver will free the segment and adjust the lengths.
That would make it impossible for an application that was looking
for the CRC.

See:

static inline void
recalculate_data_len(struct rte_mbuf *first_seg, struct rte_mbuf *last_seg,
		    struct rte_mbuf *rxm, struct hns3_rx_queue *rxq,
		    uint16_t data_len)
{
	uint8_t crc_len = rxq->crc_len;

	if (data_len <= crc_len) {
		rte_pktmbuf_free_seg(rxm);
		first_seg->nb_segs--;
		last_seg->data_len = (uint16_t)(last_seg->data_len -
			(crc_len - data_len));
		last_seg->next = NULL;
	} else
		rxm->data_len = (uint16_t)(data_len - crc_len);
}