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

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

On Wed, Jul 15, 2026 at 09:37:42AM +0000, Loktionov, Aleksandr wrote:
> 
> 
> > -----Original Message-----
> > From: Intel-wired-lan <intel-wired-lan-bounces@osuosl.org> On Behalf
> > Of Chenguang Zhao
> > Sent: Tuesday, July 14, 2026 4:51 AM
> > To: Nguyen, Anthony L <anthony.l.nguyen@intel.com>; Kitszel,
> > Przemyslaw <przemyslaw.kitszel@intel.com>; andrew+netdev@lunn.ch;
> > davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
> > pabeni@redhat.com
> > Cc: intel-wired-lan@lists.osuosl.org; netdev@vger.kernel.org;
> > chenguang.zhao@linux.dev; Chenguang Zhao <zhaochenguang@kylinos.cn>
> > Subject: [Intel-wired-lan] [PATCH net] i40e: xsk: fix multi-buffer
> > XDP_PASS skb construction
> > 
> > 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.
> > 
> >  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
> 
> Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>

Aleks, may I ask what is your intent here? Do you disagree with suggestion
I had regarding this change?

We could go with this as-is, right, but given we have a helper available
to do exactly what this patch touches, I think we could kill two birds
with one stone by removing home-grown code. However one might argue that
such change is a -next material.

Anyways, some explanation would be better than dropping plain tag.

>