Subject: Re: [RFC PATCH] bpf: cpumap: report queue_index to xdp_rxq_info

From: "Jose A. Perez de Azpillaga" <[email-masked]>
Date: Sat, 11 Apr 2026 21:10:40 +0200

On Sat, Apr 11, 2026 at 11:09:56AM -0700, Alexei Starovoitov wrote:
> On Sat, Apr 11, 2026 at 10:51 AM Jose A. Perez de Azpillaga
> <[email-masked]> wrote:
> >
> > When a packet is redirected to a CPU map entry,
> > cpu_map_bpf_prog_run_xdp() reconstructs a minimal xdp_rxq_info from
> > xdp_frame fields (dev_rx and mem_type) before re-running the BPF program
> > on the target CPU. However, queue_index was never preserved across the
> > CPU boundary, so BPF programs running in cpumap context always observe
> > ctx->rx_queue_index == 0, regardless of which hardware queue originally
> > received the packet.
> >
> > Fix this by storing the originating queue_index in struct xdp_frame,
> > following the same pattern already established for dev_rx and mem_type.
> > The field is populated from rxq->queue_index in
> > xdp_convert_buff_to_frame() during NAPI context, when the rxq_info is
> > still valid, and restored into the reconstructed rxq_info in
> > cpu_map_bpf_prog_run_xdp().
> >
> > Also use xdpf->queue_index in __xdp_build_skb_from_frame() to call
> > skb_record_rx_queue(), which was previously listed as missing
> > information in that function's comment.
> >
> > Also propagate queue_index in dpaa_a050385_wa_xdpf(), which manually
> > constructs a new xdp_frame from an uninitialized page. Without this,
> > queue_index would contain stale data from the page allocator.
> >
> > Signed-off-by: Jose A. Perez de Azpillaga <[email-masked]>
> > ---
> > Note: this patch was only compiled, not tested.
> >
> >  drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 1 +
> >  include/net/xdp.h                              | 4 +++-
> >  kernel/bpf/cpumap.c                            | 2 +-
> >  net/core/xdp.c                                 | 2 +-
> >  4 files changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > index 3edc8d142dd5..00e36b0ac74d 100644
> > --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > @@ -2281,6 +2281,7 @@ static int dpaa_a050385_wa_xdpf(struct dpaa_priv *priv,
> >         new_xdpf->headroom = priv->tx_headroom;
> >         new_xdpf->frame_sz = DPAA_BP_RAW_SIZE;
> >         new_xdpf->mem_type = MEM_TYPE_PAGE_ORDER0;
> > +       new_xdpf->queue_index = xdpf->queue_index;
> >
> >         /* Release the initial buffer */
> >         xdp_return_frame_rx_napi(xdpf);
> > diff --git a/include/net/xdp.h b/include/net/xdp.h
> > index aa742f413c35..6db10e6a8864 100644
> > --- a/include/net/xdp.h
> > +++ b/include/net/xdp.h
> > @@ -297,10 +297,11 @@ struct xdp_frame {
> >         u32 headroom;
> >         u32 metasize; /* uses lower 8-bits */
> >         /* Lifetime of xdp_rxq_info is limited to NAPI/enqueue time,
> > -        * while mem_type is valid on remote CPU.
> > +        * while mem_type and queue_index are valid on remote CPU.
> >          */
> >         enum xdp_mem_type mem_type:32;
> >         struct net_device *dev_rx; /* used by cpumap */
> > +       u32 queue_index; /* used by cpumap */
> >         u32 frame_sz;
> >         u32 flags; /* supported values defined in xdp_buff_flags */
> >  };
> > @@ -441,6 +442,7 @@ struct xdp_frame *xdp_convert_buff_to_frame(struct xdp_buff *xdp)
> >
> >         /* rxq only valid until napi_schedule ends, convert to xdp_mem_type */
> >         xdp_frame->mem_type = xdp->rxq->mem.type;
> > +       xdp_frame->queue_index = xdp->rxq->queue_index;
> >
> >         return xdp_frame;
> >  }
> > diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> > index 5e59ab896f05..448da572de9a 100644
> > --- a/kernel/bpf/cpumap.c
> > +++ b/kernel/bpf/cpumap.c
> > @@ -197,7 +197,7 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
> >
> >                 rxq.dev = xdpf->dev_rx;
> >                 rxq.mem.type = xdpf->mem_type;
> > -               /* TODO: report queue_index to xdp_rxq_info */
> > +               rxq.queue_index = xdpf->queue_index;
>
> This is like 5th time people attempt to address this TODO.
>
> Just remove that comment. Don't send broken patches.

oh... okay. but I have a question, since the bot detected something
I didn't and queue_index should be propagated in
xdp_convert_zc_to_xdp_frame(), or maybe intentional?

is it better to do as you said, removing the comment, or doing what the
bot said with proper test?

--
regards,
jose a. p-a