Re: [RFC PATCHv2 1/1] idpf: Fix header clobber in IDPF with SWIOTLB enabled

[Alexander Lobakin <aleksander.lobakin@intel.com>]

From: Steve Rutherford <srutherford@google.com>
Date: Fri, 27 Feb 2026 20:34:57 +0000

> When SWIOTLB and header split are enabled, IDPF sees empty packets in the
> rx queue.
> 
> This is caused by libeth_rx_sync_for_cpu clobbering the synthesized header
> in the workaround (i.e. overflow) path. After the header is synthesized by
> idpf_rx_hsplit_wa, the sync call pulls from the empty SWIOTLB buffer,
> effectively zeroing out the buffer.
> 
> This skips the extra sync in the workaround path in most cases. The one
> exception is that it calls sync to trigger a recycle the header buffer when
> it fails to find a header in the payload.
> 
> Fixes: 90912f9f4f2d1 ("idpf: convert header split mode to libeth + napi_build_skb()")
> Signed-off-by: Steve Rutherford <srutherford@google.com>
> ---
>  drivers/net/ethernet/intel/idpf/idpf_txrx.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/idpf/idpf_txrx.c b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> index 3ddf7b1e85ef..946203a6bd86 100644
> --- a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> +++ b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> @@ -3007,9 +3007,14 @@ static int idpf_rx_splitq_clean(struct idpf_rx_queue *rxq, int budget)
>  			u64_stats_update_begin(&rxq->stats_sync);
>  			u64_stats_inc(&rxq->q_stats.hsplit_buf_ovf);
>  			u64_stats_update_end(&rxq->stats_sync);
> -		}
>  
> -		if (libeth_rx_sync_for_cpu(hdr, hdr_len)) {
> +			/* Recycle the hdr buffer if unused.*/
> +			if (!hdr_len)
> +				libeth_rx_sync_for_cpu(hdr, 0);
> +		} else if (!libeth_rx_sync_for_cpu(hdr, hdr_len))
> +			hdr_len = 0;
> +
> +		if (hdr_len) {

This is for a very old tree I believe? We now have
libeth_xdp_process_buff() there for quite some time already.

>  			skb = idpf_rx_build_skb(hdr, hdr_len);
>  			if (!skb)
>  				break;

Thanks,
Olek