Re: [PATCH net-next] i40e: xsk: use xdp_build_skb_from_zc() for XDP_PASS

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Fri, Jul 24, 2026 at 10:01:25AM +0800, Chenguang Zhao wrote:
> From: Chenguang Zhao <zhaochenguang@kylinos.cn>
> 
> Replace the driver-local i40e_construct_skb_zc() with the common
> helper xdp_build_skb_from_zc(). 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().
> 
> Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
> Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
> ---
> The earlier patch was discussed on the net tree.
>     v2:
>     https://lore.kernel.org/all/20260717012416.168107-1-chenguang.zhao@linux.dev/
>     v1:
>     https://lore.kernel.org/all/20260714025112.284724-1-chenguang.zhao@linux.dev/
> Because older kernels do not have xdp_build_skb_from_zc(), only the bugfix goes
> to net; the refactor lands on net-next.
> 
>  drivers/net/ethernet/intel/i40e/i40e_xsk.c | 74 +++-------------------
>  1 file changed, 9 insertions(+), 65 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> index 9f47388eaba5..13932b36142d 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> @@ -3,6 +3,7 @@
>  
>  #include <linux/bpf_trace.h>
>  #include <linux/unroll.h>
> +#include <net/xdp.h>
>  #include <net/xdp_sock_drv.h>
>  #include "i40e_txrx_common.h"
>  #include "i40e_xsk.h"
> @@ -277,70 +278,6 @@ bool i40e_alloc_rx_buffers_zc(struct i40e_ring *rx_ring, u16 count)
>  	return count == nb_buffs;
>  }
>  
> -/**
> - * i40e_construct_skb_zc - Create skbuff from zero-copy Rx buffer
> - * @rx_ring: Rx ring
> - * @xdp: xdp_buff
> - *
> - * This functions allocates a new skb from a zero-copy Rx buffer.
> - *
> - * Returns the skb, or NULL on failure.
> - **/
> -static struct sk_buff *i40e_construct_skb_zc(struct i40e_ring *rx_ring,
> -					     struct xdp_buff *xdp)
> -{
> -	unsigned int totalsize = xdp->data_end - xdp->data_meta;
> -	unsigned int metasize = xdp->data - xdp->data_meta;
> -	struct skb_shared_info *sinfo = NULL;
> -	struct sk_buff *skb;
> -	u32 nr_frags = 0;
> -
> -	if (unlikely(xdp_buff_has_frags(xdp))) {
> -		sinfo = xdp_get_shared_info_from_buff(xdp);
> -		nr_frags = sinfo->nr_frags;
> -	}
> -	net_prefetch(xdp->data_meta);
> -
> -	/* allocate a skb to store the frags */
> -	skb = napi_alloc_skb(&rx_ring->q_vector->napi, totalsize);
> -	if (unlikely(!skb))
> -		goto out;
> -
> -	memcpy(__skb_put(skb, totalsize), xdp->data_meta,
> -	       ALIGN(totalsize, sizeof(long)));
> -
> -	if (metasize) {
> -		skb_metadata_set(skb, metasize);
> -		__skb_pull(skb, metasize);
> -	}
> -
> -	if (likely(!xdp_buff_has_frags(xdp)))
> -		goto out;
> -
> -	for (int i = 0; i < nr_frags; i++) {
> -		struct skb_shared_info *skinfo = skb_shinfo(skb);
> -		skb_frag_t *frag = &sinfo->frags[i];
> -		struct page *page;
> -		void *addr;
> -
> -		page = dev_alloc_page();
> -		if (!page) {
> -			dev_kfree_skb(skb);
> -			return NULL;
> -		}
> -		addr = page_to_virt(page);
> -
> -		memcpy(addr, skb_frag_page(frag), skb_frag_size(frag));
> -
> -		__skb_fill_page_desc_noacc(skinfo, skinfo->nr_frags++,
> -					   addr, 0, skb_frag_size(frag));
> -	}
> -
> -out:
> -	xsk_buff_free(xdp);
> -	return skb;
> -}
> -
>  static void i40e_handle_xdp_result_zc(struct i40e_ring *rx_ring,
>  				      struct xdp_buff *xdp_buff,
>  				      union i40e_rx_desc *rx_desc,
> @@ -372,14 +309,21 @@ 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().
> +		 */
> +		__skb_push(skb, skb->data - skb_mac_header(skb));

This feels a bit counter-productive. We would end up calling
skb_record_rx_queue() and eth_type_trans() twice. Maybe we should open
code the bits from i40e_process_skb_fields() excluding the two above?

Or pull it out to internal function and make i40e_process_skb_fields()
call it.

> +
>  		if (eth_skb_pad(skb)) {
>  			*rx_packets = 0;
>  			*rx_bytes = 0;
> -- 
> 2.25.1
> 
>