[PATCH net v3] i40e: xsk: fix multi-buffer XDP_PASS skb construction

From: Chenguang Zhao <redacted>

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 <redacted>
Reviewed-by: Aleksandr Loktionov <redacted>
Reviewed-by: Jason Xing <redacted>
---
v3:
 - To ensure backport compatibility for stable branches, this patch solely
   addresses bug fixes. The refactored version that replaces i40e_construct_skb_zc()
   with xdp_build_skb_from_zc() will be submitted to the -next tree. 
v2:
 - https://lore.kernel.org/all/20260717012416.168107-1-chenguang.zhao@linux.dev/ (local)
v1:
 - https://lore.kernel.org/all/20260714025112.284724-1-chenguang.zhao@linux.dev/ (local)

 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