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

["Jose A. Perez de Azpillaga" <azpijr@gmail.com>]

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 <azpijr@gmail.com>
---
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;

 		xdp_convert_frame_to_buff(xdpf, &xdp);

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 9890a30584ba..326e3057ed7f 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -829,11 +829,11 @@ struct sk_buff *__xdp_build_skb_from_frame(struct xdp_frame *xdpf,

 	/* Essential SKB info: protocol and skb->dev */
 	skb->protocol = eth_type_trans(skb, dev);
+	skb_record_rx_queue(skb, xdpf->queue_index);

 	/* Optional SKB info, currently missing:
 	 * - HW checksum info		(skb->ip_summed)
 	 * - HW RX hash			(skb_set_hash)
-	 * - RX ring dev queue index	(skb_record_rx_queue)
 	 */

 	if (xdpf->mem_type == MEM_TYPE_PAGE_POOL)
--
2.53.0