nfp: bpf: rework MTU checking

If control channel MTU is too low to support map operations a warning
will be printed. This is not enough, we want to make sure probe fails
in such scenario, as this would clearly be a faulty configuration.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

drivers/net/ethernet/netronome/nfp/bpf/cmsg.c

@@ -267,11 +267,15 @@ int nfp_bpf_ctrl_getnext_entry(struct bpf_offloaded_map *offmap,
 				     key, NULL, 0, next_key, NULL);
 }
 
+unsigned int nfp_bpf_ctrl_cmsg_min_mtu(struct nfp_app_bpf *bpf)
+{
+	return max(nfp_bpf_cmsg_map_req_size(bpf, 1),
+		   nfp_bpf_cmsg_map_reply_size(bpf, 1));
+}
+
 unsigned int nfp_bpf_ctrl_cmsg_mtu(struct nfp_app_bpf *bpf)
 {
-	return max3((unsigned int)NFP_NET_DEFAULT_MTU,
-		    nfp_bpf_cmsg_map_req_size(bpf, 1),
-		    nfp_bpf_cmsg_map_reply_size(bpf, 1));
+	return max(NFP_NET_DEFAULT_MTU, nfp_bpf_ctrl_cmsg_min_mtu(bpf));
 }
 
 void nfp_bpf_ctrl_msg_rx(struct nfp_app *app, struct sk_buff *skb)

drivers/net/ethernet/netronome/nfp/bpf/main.c

@@ -415,6 +415,20 @@ static void nfp_bpf_ndo_uninit(struct nfp_app *app, struct net_device *netdev)
 	bpf_offload_dev_netdev_unregister(bpf->bpf_dev, netdev);
 }
 
+static int nfp_bpf_start(struct nfp_app *app)
+{
+	struct nfp_app_bpf *bpf = app->priv;
+
+	if (app->ctrl->dp.mtu < nfp_bpf_ctrl_cmsg_min_mtu(bpf)) {
+		nfp_err(bpf->app->cpp,
+			"ctrl channel MTU below min required %u < %u\n",
+			app->ctrl->dp.mtu, nfp_bpf_ctrl_cmsg_min_mtu(bpf));
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int nfp_bpf_init(struct nfp_app *app)
 {
 	struct nfp_app_bpf *bpf;
@@ -488,6 +502,7 @@ const struct nfp_app_type app_bpf = {
 
 	.init		= nfp_bpf_init,
 	.clean		= nfp_bpf_clean,
+	.start		= nfp_bpf_start,
 
 	.check_mtu	= nfp_bpf_check_mtu,
 

drivers/net/ethernet/netronome/nfp/bpf/main.h

@@ -564,6 +564,7 @@ nfp_bpf_goto_meta(struct nfp_prog *nfp_prog, struct nfp_insn_meta *meta,
 
 void *nfp_bpf_relo_for_vnic(struct nfp_prog *nfp_prog, struct nfp_bpf_vnic *bv);
 
+unsigned int nfp_bpf_ctrl_cmsg_min_mtu(struct nfp_app_bpf *bpf);
 unsigned int nfp_bpf_ctrl_cmsg_mtu(struct nfp_app_bpf *bpf);
 long long int
 nfp_bpf_ctrl_alloc_map(struct nfp_app_bpf *bpf, struct bpf_map *map);

drivers/net/ethernet/netronome/nfp/nfp_net.h

@@ -66,7 +66,7 @@
 #define NFP_NET_MAX_DMA_BITS	40
 
 /* Default size for MTU and freelist buffer sizes */
-#define NFP_NET_DEFAULT_MTU		1500
+#define NFP_NET_DEFAULT_MTU		1500U
 
 /* Maximum number of bytes prepended to a packet */
 #define NFP_NET_MAX_PREPEND		64

drivers/net/ethernet/netronome/nfp/nfp_net_common.c

@@ -4116,14 +4116,7 @@ int nfp_net_init(struct nfp_net *nn)
 
 	/* Set default MTU and Freelist buffer size */
 	if (!nfp_net_is_data_vnic(nn) && nn->app->ctrl_mtu) {
-		if (nn->app->ctrl_mtu <= nn->max_mtu) {
-			nn->dp.mtu = nn->app->ctrl_mtu;
-		} else {
-			if (nn->app->ctrl_mtu != NFP_APP_CTRL_MTU_MAX)
-				nn_warn(nn, "app requested MTU above max supported %u > %u\n",
-					nn->app->ctrl_mtu, nn->max_mtu);
-			nn->dp.mtu = nn->max_mtu;
-		}
+		nn->dp.mtu = min(nn->app->ctrl_mtu, nn->max_mtu);
 	} else if (nn->max_mtu < NFP_NET_DEFAULT_MTU) {
 		nn->dp.mtu = nn->max_mtu;
 	} else {