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

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

On Thu, Jul 23, 2026 at 03:59:44PM +0800, Jason Xing wrote:
> On Thu, Jul 23, 2026 at 3:02 PM Chenguang Zhao <chenguang.zhao@linux.dev> wrote:
> >
> > Thanks for the clarification.
> 
> Please do not top-post.
> 
> >
> > I agree: the minimal bugfix belongs in -net for stable backportability, and the conversion to xdp_build_skb_from_zc() belongs in -next.
> 
> Right. That's what I meant. But I will let Maciej/Tony/Olek make the decision.

Thanks Jason - agree with the logistics you are proposing.

> 
> >
> > Please apply the existing v1 bugfix to -net:
> >
> >      https://lore.kernel.org/all/20260714025112.284724-1-chenguang.zhao@linux.dev/
> 
> If we eventually need this patch, then you will send a v3 patch
> instead of asking maintainers to pick it up :)
> 
> And feel free to add:
> Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
> 
> >
> > It already has :
> >
> >     Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
> >
> > I will drop v2 as a Fixes candidate.
> >
> > In parallel, I will send a separate net-next series (as v1) that replaces
> >
> > i40e_construct_skb_zc() with xdp_build_skb_from_zc(), based on
> >
> > net-next. That patch will not carry a Fixes tag.
> 
> As to this version, my tag still holds:
> Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
> 
> Thanks,
> Jason
> 
> >
> >
> > Thanks,
> >
> > Chenguang
> >
> >
> > 在 2026/7/22 07:15, Jason Xing 写道:
> > > 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
> > >>
> > >>
>