[PATCH net v2] i40e: xsk: fix multi-buffer XDP_PASS skb construction

[PATCH net v2] i40e: xsk: fix multi-buffer XDP_PASS skb construction

[Chenguang Zhao]

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>
---
Revised as suggested by Maciej:
 - Replace i40e_construct_skb_zc() with xdp_build_skb_from_zc()

v1:
 https://lore.kernel.org/all/20260714025112.284724-1-chenguang.zhao@linux.dev/

 drivers/net/ethernet/intel/i40e/i40e_xsk.c | 73 +++-------------------
 1 file changed, 8 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..1319a5c22625 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 +309,20 @@ 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().
+		 */
+		__skb_push(skb, skb->data - skb_mac_header(skb));
+
 		if (eth_skb_pad(skb)) {
 			*rx_packets = 0;
 			*rx_bytes = 0;
-- 
2.25.1

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

[Alexander Lobakin]

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

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

[Jason Xing]

On Fri, Jul 17, 2026 at 9:24 AM Chenguang Zhao <chenguang.zhao@linux.dev> wrote:
>
> 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>
> ---
> Revised as suggested by Maciej:
>  - Replace i40e_construct_skb_zc() with xdp_build_skb_from_zc()

I might have a different opinion on this patch: yes, it actually
belongs to -next material. The process should be like: 1) fix the
issues by v1, 2) refactor it by v2. The reason behind that is the
helper was introduced in 2024 while the home-grown part was in 2023,
which means it doesn't help for stable steam to cherry-pick the patch
in older kernels like 6.6[1].

[1]: https://www.kernel.org/

Thanks,
Jason

>
> v1:
>  https://lore.kernel.org/all/20260714025112.284724-1-chenguang.zhao@linux.dev/
>
>  drivers/net/ethernet/intel/i40e/i40e_xsk.c | 73 +++-------------------
>  1 file changed, 8 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..1319a5c22625 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 +309,20 @@ 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().
> +                */
> +               __skb_push(skb, skb->data - skb_mac_header(skb));
> +
>                 if (eth_skb_pad(skb)) {
>                         *rx_packets = 0;
>                         *rx_bytes = 0;
> --
> 2.25.1
>
>