mac80211: add fast-rx path

The regular RX path has a lot of code, but with a few
assumptions on the hardware it's possible to reduce the
amount of code significantly. Currently the assumptions
on the driver are the following:
 * hardware/driver reordering buffer (if supporting aggregation)
 * hardware/driver decryption & PN checking (if using encryption)
 * hardware/driver did de-duplication
 * hardware/driver did A-MSDU deaggregation
 * AP_LINK_PS is used (in AP mode)
 * no client powersave handling in mac80211 (in client mode)

of which some are actually checked per packet:
 * de-duplication
 * PN checking
 * decryption
and additionally packets must
 * not be A-MSDU (have been deaggregated by driver/device)
 * be data packets
 * not be fragmented
 * be unicast
 * have RFC 1042 header

Additionally dynamically we assume:
 * no encryption or CCMP/GCMP, TKIP/WEP/other not allowed
 * station must be authorized
 * 4-addr format not enabled

Some data needed for the RX path is cached in a new per-station
"fast_rx" structure, so that we only need to look at this and
the packet, no other memory when processing packets on the fast
RX path.

After doing the above per-packet checks, the data path collapses
down to a pretty simple conversion function taking advantage of
the data cached in the small fast_rx struct.

This should speed up the RX processing, and will make it easier
to reason about parallelizing RX (for which statistics will need
to be per-CPU still.)
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/linux/ieee80211.h

@@ -638,6 +638,16 @@ static inline bool ieee80211_is_first_frag(__le16 seq_ctrl)
 	return (seq_ctrl & cpu_to_le16(IEEE80211_SCTL_FRAG)) == 0;
 }
 
+/**
+ * ieee80211_is_frag - check if a frame is a fragment
+ * @hdr: 802.11 header of the frame
+ */
+static inline bool ieee80211_is_frag(struct ieee80211_hdr *hdr)
+{
+	return ieee80211_has_morefrags(hdr->frame_control) ||
+	       hdr->seq_ctrl & cpu_to_le16(IEEE80211_SCTL_FRAG);
+}
+
 struct ieee80211s_hdr {
 	u8 flags;
 	u8 ttl;

net/mac80211/cfg.c

@@ -65,11 +65,13 @@ static int ieee80211_change_iface(struct wiphy *wiphy,
 		return ret;
 
 	if (type == NL80211_IFTYPE_AP_VLAN &&
-	    params && params->use_4addr == 0)
+	    params && params->use_4addr == 0) {
 		RCU_INIT_POINTER(sdata->u.vlan.sta, NULL);
-	else if (type == NL80211_IFTYPE_STATION &&
-		 params && params->use_4addr >= 0)
+		ieee80211_check_fast_rx_iface(sdata);
+	} else if (type == NL80211_IFTYPE_STATION &&
+		   params && params->use_4addr >= 0) {
 		sdata->u.mgd.use_4addr = params->use_4addr;
+	}
 
 	if (sdata->vif.type == NL80211_IFTYPE_MONITOR && flags) {
 		struct ieee80211_local *local = sdata->local;
@@ -1367,6 +1369,7 @@ static int ieee80211_change_station(struct wiphy *wiphy,
 
 			rcu_assign_pointer(vlansdata->u.vlan.sta, sta);
 			new_4addr = true;
+			__ieee80211_check_fast_rx_iface(vlansdata);
 		}
 
 		if (sta->sdata->vif.type == NL80211_IFTYPE_AP_VLAN &&
@@ -1889,6 +1892,7 @@ static int ieee80211_change_bss(struct wiphy *wiphy,
 			sdata->flags |= IEEE80211_SDATA_DONT_BRIDGE_PACKETS;
 		else
 			sdata->flags &= ~IEEE80211_SDATA_DONT_BRIDGE_PACKETS;
+		ieee80211_check_fast_rx_iface(sdata);
 	}
 
 	if (params->ht_opmode >= 0) {

net/mac80211/ieee80211_i.h

@@ -1494,6 +1494,11 @@ u64 ieee80211_mgmt_tx_cookie(struct ieee80211_local *local);
 int ieee80211_attach_ack_skb(struct ieee80211_local *local, struct sk_buff *skb,
 			     u64 *cookie, gfp_t gfp);
 
+void ieee80211_check_fast_rx(struct sta_info *sta);
+void __ieee80211_check_fast_rx_iface(struct ieee80211_sub_if_data *sdata);
+void ieee80211_check_fast_rx_iface(struct ieee80211_sub_if_data *sdata);
+void ieee80211_clear_fast_rx(struct sta_info *sta);
+
 /* STA code */
 void ieee80211_sta_setup_sdata(struct ieee80211_sub_if_data *sdata);
 int ieee80211_mgd_auth(struct ieee80211_sub_if_data *sdata,

net/mac80211/key.c

@@ -338,6 +338,7 @@ static void ieee80211_key_replace(struct ieee80211_sub_if_data *sdata,
 		} else {
 			rcu_assign_pointer(sta->gtk[idx], new);
 		}
+		ieee80211_check_fast_rx(sta);
 	} else {
 		defunikey = old &&
 			old == key_mtx_dereference(sdata->local,

net/mac80211/mlme.c

@@ -2217,6 +2217,7 @@ static void ieee80211_mgd_probe_ap_send(struct ieee80211_sub_if_data *sdata)
 	const u8 *ssid;
 	u8 *dst = ifmgd->associated->bssid;
 	u8 unicast_limit = max(1, max_probe_tries - 3);
+	struct sta_info *sta;
 
 	/*
 	 * Try sending broadcast probe requests for the last three
@@ -2235,6 +2236,14 @@ static void ieee80211_mgd_probe_ap_send(struct ieee80211_sub_if_data *sdata)
 	 */
 	ifmgd->probe_send_count++;
 
+	if (dst) {
+		mutex_lock(&sdata->local->sta_mtx);
+		sta = sta_info_get(sdata, dst);
+		if (!WARN_ON(!sta))
+			ieee80211_check_fast_rx(sta);
+		mutex_unlock(&sdata->local->sta_mtx);
+	}
+
 	if (ieee80211_hw_check(&sdata->local->hw, REPORTS_TX_ACK_STATUS)) {
 		ifmgd->nullfunc_failed = false;
 		ieee80211_send_nullfunc(sdata->local, sdata, false);

net/mac80211/sta_info.c

@@ -1874,6 +1874,7 @@ int sta_info_move_state(struct sta_info *sta,
 				atomic_dec(&sta->sdata->bss->num_mcast_sta);
 			clear_bit(WLAN_STA_AUTHORIZED, &sta->_flags);
 			ieee80211_clear_fast_xmit(sta);
+			ieee80211_clear_fast_rx(sta);
 		}
 		break;
 	case IEEE80211_STA_AUTHORIZED:
@@ -1884,6 +1885,7 @@ int sta_info_move_state(struct sta_info *sta,
 				atomic_inc(&sta->sdata->bss->num_mcast_sta);
 			set_bit(WLAN_STA_AUTHORIZED, &sta->_flags);
 			ieee80211_check_fast_xmit(sta);
+			ieee80211_check_fast_rx(sta);
 		}
 		break;
 	default:

net/mac80211/sta_info.h

@@ -285,6 +285,38 @@ struct ieee80211_fast_tx {
 	struct rcu_head rcu_head;
 };
 
+/**
+ * struct ieee80211_fast_rx - RX fastpath information
+ * @dev: netdevice for reporting the SKB
+ * @vif_type: (P2P-less) interface type of the original sdata (sdata->vif.type)
+ * @vif_addr: interface address
+ * @rfc1042_hdr: copy of the RFC 1042 SNAP header (to have in cache)
+ * @control_port_protocol: control port protocol copied from sdata
+ * @expected_ds_bits: from/to DS bits expected
+ * @icv_len: length of the MIC if present
+ * @key: bool indicating encryption is expected (key is set)
+ * @sta_notify: notify the MLME code (once)
+ * @internal_forward: forward froms internally on AP/VLAN type interfaces
+ * @da_offs: offset of the DA in the header (for header conversion)
+ * @sa_offs: offset of the SA in the header (for header conversion)
+ * @rcu_head: RCU head for freeing this structure
+ */
+struct ieee80211_fast_rx {
+	struct net_device *dev;
+	enum nl80211_iftype vif_type;
+	u8 vif_addr[ETH_ALEN] __aligned(2);
+	u8 rfc1042_hdr[6] __aligned(2);
+	__be16 control_port_protocol;
+	__le16 expected_ds_bits;
+	u8 icv_len;
+	u8 key:1,
+	   sta_notify:1,
+	   internal_forward:1;
+	u8 da_offs, sa_offs;
+
+	struct rcu_head rcu_head;
+};
+
 /**
  * struct mesh_sta - mesh STA information
  * @plink_lock: serialize access to plink fields
@@ -391,6 +423,7 @@ DECLARE_EWMA(signal, 1024, 8)
  * @cipher_scheme: optional cipher scheme for this station
  * @reserved_tid: reserved TID (if any, otherwise IEEE80211_TID_UNRESERVED)
  * @fast_tx: TX fastpath information
+ * @fast_rx: RX fastpath information
  * @tdls_chandef: a TDLS peer can have a wider chandef that is compatible to
  *	the BSS one.
  * @tx_stats: TX statistics
@@ -414,6 +447,7 @@ struct sta_info {
 	spinlock_t lock;
 
 	struct ieee80211_fast_tx __rcu *fast_tx;
+	struct ieee80211_fast_rx __rcu *fast_rx;
 
 #ifdef CONFIG_MAC80211_MESH
 	struct mesh_sta *mesh;