ionic: Allow XDP program to be hot swapped

Using examples of other driver(s), add the ability to hot-swap an XDP
program without having to reconfigure the queues. To prevent the
q->xdp_prog to be read/written more than once use READ_ONCE() and
WRITE_ONCE() on the q->xdp_prog.

The q->xdp_prog was being checked in multiple different for loops in the
hot path. The change to allow xdp_prog hot swapping created the
possibility for many READ_ONCE(q->xdp_prog) calls during a single napi
callback. Refactor the Rx napi handling to allow a previous
READ_ONCE(q->xdp_prog) (or NULL for hwstamp_rxq) to be passed into the
relevant functions.

Also, move other Rx related hotpath handling into the newly created
ionic_rx_cq_service() function to reduce the scope of the xdp_prog
local variable and put all Rx handling in one function similar to Tx.

Signed-off-by: Brett Creeley <[email protected]>
Signed-off-by: Shannon Nelson <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: brettcreeley

drivers/net/ethernet/pensando/ionic/ionic_lif.c

@@ -1074,7 +1074,7 @@ int ionic_lif_create_hwstamp_rxq(struct ionic_lif *lif)
 			goto err_qcq_init;
 
 		if (test_bit(IONIC_LIF_F_UP, lif->state)) {
-			ionic_rx_fill(&rxq->q);
+			ionic_rx_fill(&rxq->q, NULL);
 			err = ionic_qcq_enable(rxq);
 			if (err)
 				goto err_qcq_enable;
@@ -2190,7 +2190,8 @@ static int ionic_txrx_enable(struct ionic_lif *lif)
 			goto err_out;
 		}
 
-		ionic_rx_fill(&lif->rxqcqs[i]->q);
+		ionic_rx_fill(&lif->rxqcqs[i]->q,
+			      READ_ONCE(lif->rxqcqs[i]->q.xdp_prog));
 		err = ionic_qcq_enable(lif->rxqcqs[i]);
 		if (err)
 			goto err_out;
@@ -2203,7 +2204,7 @@ static int ionic_txrx_enable(struct ionic_lif *lif)
 	}
 
 	if (lif->hwstamp_rxq) {
-		ionic_rx_fill(&lif->hwstamp_rxq->q);
+		ionic_rx_fill(&lif->hwstamp_rxq->q, NULL);
 		err = ionic_qcq_enable(lif->hwstamp_rxq);
 		if (err)
 			goto err_out_hwstamp_rx;
@@ -2746,7 +2747,7 @@ static void ionic_xdp_rxqs_prog_update(struct ionic_lif *lif)
 	for (i = 0; i < lif->ionic->nrxqs_per_lif && lif->rxqcqs[i]; i++) {
 		struct ionic_queue *q = &lif->rxqcqs[i]->q;
 
-		q->xdp_prog = xdp_prog;
+		WRITE_ONCE(q->xdp_prog, xdp_prog);
 	}
 }
 
@@ -2777,6 +2778,9 @@ static int ionic_xdp_config(struct net_device *netdev, struct netdev_bpf *bpf)
 
 	if (!netif_running(netdev)) {
 		old_prog = xchg(&lif->xdp_prog, bpf->prog);
+	} else if (lif->xdp_prog && bpf->prog) {
+		old_prog = xchg(&lif->xdp_prog, bpf->prog);
+		ionic_xdp_rxqs_prog_update(lif);
 	} else {
 		struct ionic_queue_params qparams;
 

drivers/net/ethernet/pensando/ionic/ionic_txrx.c

@@ -602,7 +602,8 @@ static bool ionic_run_xdp(struct ionic_rx_stats *stats,
 
 static void ionic_rx_clean(struct ionic_queue *q,
 			   struct ionic_rx_desc_info *desc_info,
-			   struct ionic_rxq_comp *comp)
+			   struct ionic_rxq_comp *comp,
+			   struct bpf_prog *xdp_prog)
 {
 	struct net_device *netdev = q->lif->netdev;
 	struct ionic_qcq *qcq = q_to_qcq(q);
@@ -631,8 +632,8 @@ static void ionic_rx_clean(struct ionic_queue *q,
 	stats->pkts++;
 	stats->bytes += len;
 
-	if (q->xdp_prog) {
-		if (ionic_run_xdp(stats, netdev, q->xdp_prog, q, desc_info->bufs, len))
+	if (xdp_prog) {
+		if (ionic_run_xdp(stats, netdev, xdp_prog, q, desc_info->bufs, len))
 			return;
 		synced = true;
 		headroom = XDP_PACKET_HEADROOM;
@@ -718,7 +719,7 @@ static void ionic_rx_clean(struct ionic_queue *q,
 		napi_gro_frags(&qcq->napi);
 }
 
-bool ionic_rx_service(struct ionic_cq *cq)
+static bool __ionic_rx_service(struct ionic_cq *cq, struct bpf_prog *xdp_prog)
 {
 	struct ionic_rx_desc_info *desc_info;
 	struct ionic_queue *q = cq->bound_q;
@@ -740,11 +741,16 @@ bool ionic_rx_service(struct ionic_cq *cq)
 	q->tail_idx = (q->tail_idx + 1) & (q->num_descs - 1);
 
 	/* clean the related q entry, only one per qc completion */
-	ionic_rx_clean(q, desc_info, comp);
+	ionic_rx_clean(q, desc_info, comp, xdp_prog);
 
 	return true;
 }
 
+bool ionic_rx_service(struct ionic_cq *cq)
+{
+	return __ionic_rx_service(cq, NULL);
+}
+
 static inline void ionic_write_cmb_desc(struct ionic_queue *q,
 					void *desc)
 {
@@ -755,7 +761,7 @@ static inline void ionic_write_cmb_desc(struct ionic_queue *q,
 		memcpy_toio(&q->cmb_txq[q->head_idx], desc, sizeof(q->cmb_txq[0]));
 }
 
-void ionic_rx_fill(struct ionic_queue *q)
+void ionic_rx_fill(struct ionic_queue *q, struct bpf_prog *xdp_prog)
 {
 	struct net_device *netdev = q->lif->netdev;
 	struct ionic_rx_desc_info *desc_info;
@@ -783,7 +789,7 @@ void ionic_rx_fill(struct ionic_queue *q)
 
 	len = netdev->mtu + VLAN_ETH_HLEN;
 
-	if (q->xdp_prog) {
+	if (xdp_prog) {
 		/* Always alloc the full size buffer, but only need
 		 * the actual frag_len in the descriptor
 		 * XDP uses space in the first buffer, so account for
@@ -964,6 +970,32 @@ static void ionic_xdp_do_flush(struct ionic_cq *cq)
 	}
 }
 
+static unsigned int ionic_rx_cq_service(struct ionic_cq *cq,
+					unsigned int work_to_do)
+{
+	struct ionic_queue *q = cq->bound_q;
+	unsigned int work_done = 0;
+	struct bpf_prog *xdp_prog;
+
+	if (work_to_do == 0)
+		return 0;
+
+	xdp_prog = READ_ONCE(q->xdp_prog);
+	while (__ionic_rx_service(cq, xdp_prog)) {
+		if (cq->tail_idx == cq->num_descs - 1)
+			cq->done_color = !cq->done_color;
+
+		cq->tail_idx = (cq->tail_idx + 1) & (cq->num_descs - 1);
+
+		if (++work_done >= work_to_do)
+			break;
+	}
+	ionic_rx_fill(q, xdp_prog);
+	ionic_xdp_do_flush(cq);
+
+	return work_done;
+}
+
 int ionic_rx_napi(struct napi_struct *napi, int budget)
 {
 	struct ionic_qcq *qcq = napi_to_qcq(napi);
@@ -974,12 +1006,8 @@ int ionic_rx_napi(struct napi_struct *napi, int budget)
 	if (unlikely(!budget))
 		return budget;
 
-	work_done = ionic_cq_service(cq, budget,
-				     ionic_rx_service, NULL, NULL);
+	work_done = ionic_rx_cq_service(cq, budget);
 
-	ionic_rx_fill(cq->bound_q);
-
-	ionic_xdp_do_flush(cq);
 	if (work_done < budget && napi_complete_done(napi, work_done)) {
 		ionic_dim_update(qcq, IONIC_LIF_F_RX_DIM_INTR);
 		flags |= IONIC_INTR_CRED_UNMASK;
@@ -1020,12 +1048,8 @@ int ionic_txrx_napi(struct napi_struct *napi, int budget)
 	if (unlikely(!budget))
 		return budget;
 
-	rx_work_done = ionic_cq_service(rxcq, budget,
-					ionic_rx_service, NULL, NULL);
-
-	ionic_rx_fill(rxcq->bound_q);
+	rx_work_done = ionic_rx_cq_service(rxcq, budget);
 
-	ionic_xdp_do_flush(rxcq);
 	if (rx_work_done < budget && napi_complete_done(napi, rx_work_done)) {
 		ionic_dim_update(rxqcq, 0);
 		flags |= IONIC_INTR_CRED_UNMASK;

drivers/net/ethernet/pensando/ionic/ionic_txrx.h

@@ -4,9 +4,11 @@
 #ifndef _IONIC_TXRX_H_
 #define _IONIC_TXRX_H_
 
+struct bpf_prog;
+
 void ionic_tx_flush(struct ionic_cq *cq);
 
-void ionic_rx_fill(struct ionic_queue *q);
+void ionic_rx_fill(struct ionic_queue *q, struct bpf_prog *xdp_prog);
 void ionic_rx_empty(struct ionic_queue *q);
 void ionic_tx_empty(struct ionic_queue *q);
 int ionic_rx_napi(struct napi_struct *napi, int budget);