Re: [Intel-wired-lan] [PATCH net v2] i40e: xsk: fix multi-buffer XDP_PASS skb construction

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

From: Chenguang Zhao <chenguang.zhao@linux.dev>
Date: Fri, 17 Jul 2026 09:24:16 +0800

> From: Chenguang Zhao <zhaochenguang@kylinos.cn>
> 
> When AF_XDP ZC receives a multi-buffer frame and XDP returns XDP_PASS,
> i40e_construct_skb_zc() copied frags incorrectly: memcpy used
> skb_frag_page() (page metadata) and __skb_fill_page_desc_noacc() was
> given a virtual address instead of a struct page *.
> 
> Drop the custom helper and use xdp_build_skb_from_zc() instead. On
> failure, free the xdp buff in the caller. Push the Ethernet header
> back before eth_skb_pad()/i40e_process_skb_fields() because
> xdp_build_skb_from_zc() already called eth_type_trans().
> 
> Fixes: 1c9ba9c14658 ("i40e: xsk: add RX multi-buffer support")
> Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>

Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>

One nit below tho.

[...]

> @@ -372,14 +309,20 @@ static void i40e_handle_xdp_result_zc(struct i40e_ring *rx_ring,
>  		 * BIT(I40E_RXD_QW1_ERROR_SHIFT). This is due to that
>  		 * SBP is *not* set in PRT_SBPVSI (default not set).
>  		 */
> -		skb = i40e_construct_skb_zc(rx_ring, xdp_buff);
> +		skb = xdp_build_skb_from_zc(xdp_buff);
>  		if (!skb) {
> +			xsk_buff_free(xdp_buff);
>  			rx_ring->rx_stats.alloc_buff_failed++;
>  			*rx_packets = 0;
>  			*rx_bytes = 0;
>  			return;
>  		}
>  
> +		/* xdp_build_skb_from_zc() already ran eth_type_trans();
> +		 * restore the header for eth_skb_pad()/process_skb_fields().
> +		 */

The netdev rules prefer generic comment style over what we used in the
past for some time already. I.e.

		/*
		 * xdp_build_skb_from_zc() ...
		 * restore ...
		 */

> +		__skb_push(skb, skb->data - skb_mac_header(skb));
> +
>  		if (eth_skb_pad(skb)) {
>  			*rx_packets = 0;
>  			*rx_bytes = 0;

Thanks,
Olek