Re: [PATCH net] i40e: xsk: fix multi-buffer XDP_PASS skb construction

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

On Tue, Jul 14, 2026 at 10:51:12AM +0800, Chenguang Zhao wrote:
> From: Chenguang Zhao <zhaochenguang@kylinos.cn>
> 
> When AF_XDP ZC receives a multi-buffer frame and the XDP program
> returns XDP_PASS, i40e_construct_skb_zc() copies frags into a new
> skb. The copy used skb_frag_page() as the memcpy source (page
> metadata instead of packet data) and passed a virtual address to
> __skb_fill_page_desc_noacc(), which expects a struct page *.
> 
> Use skb_frag_address() for the copy, attach frags with
> skb_add_rx_frag() so len/data_len/truesize are updated, and on
> dev_alloc_page() failure free the skb via the shared out path so
> xsk_buff_free() still runs and previously attached pages are
> released by kfree_skb.
> 
> Fixes: 1c9ba9c14658 ("i40e: xsk: add RX multi-buffer support")
> Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
> ---
>  - Fix memcpy source: use skb_frag_address() instead of skb_frag_page(),
>    which was copying page metadata rather than packet data.
> 
>  - Fix frag attachment: pass the allocated struct page * to the skb frag
>    helper instead of the page virtual address.
> 
>  - Use skb_add_rx_frag() so skb->len, data_len and truesize are updated
>    when attaching copied frags.
> 
>  - On mid-loop dev_alloc_page() failure, go through the shared out path
>    so previously attached pages are released via kfree_skb and
>    xsk_buff_free() is still called.

Hi!

I assume this is a fix, so you should include your target tree in patch
subject (net) plus Fixes: tag.

However, could you take a look if we could use xdp_build_skb_from_zc() and
wipe out i40e_construct_skb_zc() altogether?

> 
>  drivers/net/ethernet/intel/i40e/i40e_xsk.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> index 9f47388eaba5..a4247710c85b 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> @@ -318,22 +318,19 @@ static struct sk_buff *i40e_construct_skb_zc(struct i40e_ring *rx_ring,
>  		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];
> +		unsigned int frag_size = skb_frag_size(frag);
>  		struct page *page;
> -		void *addr;
>  
>  		page = dev_alloc_page();
>  		if (!page) {
>  			dev_kfree_skb(skb);
> -			return NULL;
> +			skb = NULL;
> +			goto out;
>  		}
> -		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));
> +		memcpy(page_to_virt(page), skb_frag_address(frag), frag_size);
> +		skb_add_rx_frag(skb, i, page, 0, frag_size, PAGE_SIZE);
>  	}
>  
>  out:
> -- 
> 2.25.1
> 
>