[PATCH 1/6] net/idpf: fix gen bit extraction in split queue AVX2 Rx

[Bruce Richardson]

On Mon, May 11, 2026 at 02:39:30PM +0530, Shaiq Wani wrote:
> The generation bit in the pktlen_gen_bufq_id field of the split queue
> completion descriptor (virtchnl2_rx_flex_desc_adv_nic_3) must be
> extracted by masking first and then shifting, not the other way around.
> 
> With shift-then-mask, the mask is applied to already-shifted bits,
> which can produce incorrect results when upper bits (packet length,
> buffer queue ID) leak into the extracted value.
> 
> Change to mask-then-shift to correctly isolate the generation bit
> before comparing it with the expected generation ID.
> 
> Fixes: 1f065f9d75ff ("net/idpf: add AVX2 Rx path for split queue config")
> Signed-off-by: Shaiq Wani <shaiq.wani at intel.com>
Acked-by: Bruce Richardson <bruce.richardson at intel.com>
> ---
>  .../net/intel/idpf/idpf_common_rxtx_avx2.c    | 20 +++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/net/intel/idpf/idpf_common_rxtx_avx2.c b/drivers/net/intel/idpf/idpf_common_rxtx_avx2.c
> index db7728afad..cd10c27a30 100644
> --- a/drivers/net/intel/idpf/idpf_common_rxtx_avx2.c
> +++ b/drivers/net/intel/idpf/idpf_common_rxtx_avx2.c
> @@ -524,8 +524,8 @@ idpf_dp_splitq_recv_pkts_avx2(void *rxq, struct rte_mbuf **rx_pkts, uint16_t nb_
>  
>  	/* check if there is at least one packet available */
>  	head_gen = rxdp->flex_adv_nic_3_wb.pktlen_gen_bufq_id;
> -	if (((head_gen >> VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_S) &
> -		 VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M) != queue->expected_gen_id)
> +	if (((head_gen & VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M) >>
> +		 VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_S) != queue->expected_gen_id)
>  		return 0;
>  
>  	for (i = 0; i < nb_pkts;
> @@ -599,17 +599,17 @@ idpf_dp_splitq_recv_pkts_avx2(void *rxq, struct rte_mbuf **rx_pkts, uint16_t nb_
>  		pktlen_gen3 = (uint16_t)_mm_extract_epi16(d3, 2);
>  
>  		valid0 = (stat0 & 1) &&
> -			 (((pktlen_gen0 >> VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_S) &
> -			   VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M) == queue->expected_gen_id);
> +			 (((pktlen_gen0 & VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M) >>
> +			   VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_S) == queue->expected_gen_id);
>  		valid1 = (stat1 & 1) &&
> -			 (((pktlen_gen1 >> VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_S) &
> -			   VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M) == queue->expected_gen_id);
> +			 (((pktlen_gen1 & VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M) >>
> +			   VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_S) == queue->expected_gen_id);
>  		valid2 = (stat2 & 1) &&
> -			 (((pktlen_gen2 >> VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_S) &
> -			   VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M) == queue->expected_gen_id);
> +			 (((pktlen_gen2 & VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M) >>
> +			   VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_S) == queue->expected_gen_id);
>  		valid3 = (stat3 & 1) &&
> -			 (((pktlen_gen3 >> VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_S) &
> -			   VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M) == queue->expected_gen_id);
> +			 (((pktlen_gen3 & VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_M) >>
> +			   VIRTCHNL2_RX_FLEX_DESC_ADV_GEN_S) == queue->expected_gen_id);
>  
>  		/* count valid descriptors (holes are impossible because
>  		 * descriptors are read in reverse order while the NIC
> -- 
> 2.34.1
>