bpf, xdp: Restructure redirect actions

The XDP_REDIRECT implementations for maps and non-maps are fairly
similar, but obviously need to take different code paths depending on
if the target is using a map or not. Today, the redirect targets for
XDP either uses a map, or is based on ifindex.

Here, the map type and id are added to bpf_redirect_info, instead of
the actual map. Map type, map item/ifindex, and the map_id (if any) is
passed to xdp_do_redirect().

For ifindex-based redirect, used by the bpf_redirect() XDP BFP helper,
a special map type/id are used. Map type of UNSPEC together with map id
equal to INT_MAX has the special meaning of an ifindex based
redirect. Note that valid map ids are 1 inclusive, INT_MAX exclusive
([1,INT_MAX[).

In addition to making the code easier to follow, using explicit type
and id in bpf_redirect_info has a slight positive performance impact
by avoiding a pointer indirection for the map type lookup, and instead
use the cacheline for bpf_redirect_info.

Since the actual map is not passed via bpf_redirect_info anymore, the
map lookup is only done in the BPF helper. This means that the
bpf_clear_redirect_map() function can be removed. The actual map item
is RCU protected.

The bpf_redirect_info flags member is not used by XDP, and not
read/written any more. The map member is only written to when
required/used, and not unconditionally.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210308112907.559576-3-bjorn.topel@gmail.com

2 files changed, 41 insertions, 31 deletions

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 008691fd3b58..b2b85b2cad8e 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -646,7 +646,8 @@ struct bpf_redirect_info {
 	u32 flags;
 	u32 tgt_index;
 	void *tgt_value;
-	struct bpf_map *map;
+	u32 map_id;
+	enum bpf_map_type map_type;
 	u32 kern_flags;
 	struct bpf_nh_params nh;
 };
@@ -1488,13 +1489,14 @@ static __always_inline int __bpf_xdp_redirect_map(struct bpf_map *map, u32 ifind
 		 * performs multiple lookups, the last one always takes
 		 * precedence.
 		 */
-		WRITE_ONCE(ri->map, NULL);
+		ri->map_id = INT_MAX; /* Valid map id idr range: [1,INT_MAX[ */
+		ri->map_type = BPF_MAP_TYPE_UNSPEC;
 		return flags;
 	}
 
-	ri->flags = flags;
 	ri->tgt_index = ifindex;
-	WRITE_ONCE(ri->map, map);
+	ri->map_id = map->id;
+	ri->map_type = map->map_type;
 
 	return XDP_REDIRECT;
 }
diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
index 76a97176ab81..fcad3645a70b 100644
--- a/include/trace/events/xdp.h
+++ b/include/trace/events/xdp.h
@@ -86,19 +86,15 @@ struct _bpf_dtab_netdev {
 };
 #endif /* __DEVMAP_OBJ_TYPE */
 
-#define devmap_ifindex(tgt, map)				\
-	(((map->map_type == BPF_MAP_TYPE_DEVMAP ||	\
-		  map->map_type == BPF_MAP_TYPE_DEVMAP_HASH)) ? \
-	  ((struct _bpf_dtab_netdev *)tgt)->dev->ifindex : 0)
-
 DECLARE_EVENT_CLASS(xdp_redirect_template,
 
 	TP_PROTO(const struct net_device *dev,
 		 const struct bpf_prog *xdp,
 		 const void *tgt, int err,
-		 const struct bpf_map *map, u32 index),
+		 enum bpf_map_type map_type,
+		 u32 map_id, u32 index),
 
-	TP_ARGS(dev, xdp, tgt, err, map, index),
+	TP_ARGS(dev, xdp, tgt, err, map_type, map_id, index),
 
 	TP_STRUCT__entry(
 		__field(int, prog_id)
@@ -111,14 +107,22 @@ DECLARE_EVENT_CLASS(xdp_redirect_template,
 	),
 
 	TP_fast_assign(
+		u32 ifindex = 0, map_index = index;
+
+		if (map_type == BPF_MAP_TYPE_DEVMAP || map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
+			ifindex = ((struct _bpf_dtab_netdev *)tgt)->dev->ifindex;
+		} else if (map_type == BPF_MAP_TYPE_UNSPEC && map_id == INT_MAX) {
+			ifindex = index;
+			map_index = 0;
+		}
+
 		__entry->prog_id	= xdp->aux->id;
 		__entry->act		= XDP_REDIRECT;
 		__entry->ifindex	= dev->ifindex;
 		__entry->err		= err;
-		__entry->to_ifindex	= map ? devmap_ifindex(tgt, map) :
-						index;
-		__entry->map_id		= map ? map->id : 0;
-		__entry->map_index	= map ? index : 0;
+		__entry->to_ifindex	= ifindex;
+		__entry->map_id		= map_id;
+		__entry->map_index	= map_index;
 	),
 
 	TP_printk("prog_id=%d action=%s ifindex=%d to_ifindex=%d err=%d"
@@ -133,45 +137,49 @@ DEFINE_EVENT(xdp_redirect_template, xdp_redirect,
 	TP_PROTO(const struct net_device *dev,
 		 const struct bpf_prog *xdp,
 		 const void *tgt, int err,
-		 const struct bpf_map *map, u32 index),
-	TP_ARGS(dev, xdp, tgt, err, map, index)
+		 enum bpf_map_type map_type,
+		 u32 map_id, u32 index),
+	TP_ARGS(dev, xdp, tgt, err, map_type, map_id, index)
 );
 
 DEFINE_EVENT(xdp_redirect_template, xdp_redirect_err,
 	TP_PROTO(const struct net_device *dev,
 		 const struct bpf_prog *xdp,
 		 const void *tgt, int err,
-		 const struct bpf_map *map, u32 index),
-	TP_ARGS(dev, xdp, tgt, err, map, index)
+		 enum bpf_map_type map_type,
+		 u32 map_id, u32 index),
+	TP_ARGS(dev, xdp, tgt, err, map_type, map_id, index)
 );
 
-#define _trace_xdp_redirect(dev, xdp, to)				\
-	 trace_xdp_redirect(dev, xdp, NULL, 0, NULL, to)
+#define _trace_xdp_redirect(dev, xdp, to)						\
+	 trace_xdp_redirect(dev, xdp, NULL, 0, BPF_MAP_TYPE_UNSPEC, INT_MAX, to)
 
-#define _trace_xdp_redirect_err(dev, xdp, to, err)			\
-	 trace_xdp_redirect_err(dev, xdp, NULL, err, NULL, to)
+#define _trace_xdp_redirect_err(dev, xdp, to, err)					\
+	 trace_xdp_redirect_err(dev, xdp, NULL, err, BPF_MAP_TYPE_UNSPEC, INT_MAX, to)
 
-#define _trace_xdp_redirect_map(dev, xdp, to, map, index)		\
-	 trace_xdp_redirect(dev, xdp, to, 0, map, index)
+#define _trace_xdp_redirect_map(dev, xdp, to, map_type, map_id, index) \
+	 trace_xdp_redirect(dev, xdp, to, 0, map_type, map_id, index)
 
-#define _trace_xdp_redirect_map_err(dev, xdp, to, map, index, err)	\
-	 trace_xdp_redirect_err(dev, xdp, to, err, map, index)
+#define _trace_xdp_redirect_map_err(dev, xdp, to, map_type, map_id, index, err) \
+	 trace_xdp_redirect_err(dev, xdp, to, err, map_type, map_id, index)
 
 /* not used anymore, but kept around so as not to break old programs */
 DEFINE_EVENT(xdp_redirect_template, xdp_redirect_map,
 	TP_PROTO(const struct net_device *dev,
 		 const struct bpf_prog *xdp,
 		 const void *tgt, int err,
-		 const struct bpf_map *map, u32 index),
-	TP_ARGS(dev, xdp, tgt, err, map, index)
+		 enum bpf_map_type map_type,
+		 u32 map_id, u32 index),
+	TP_ARGS(dev, xdp, tgt, err, map_type, map_id, index)
 );
 
 DEFINE_EVENT(xdp_redirect_template, xdp_redirect_map_err,
 	TP_PROTO(const struct net_device *dev,
 		 const struct bpf_prog *xdp,
 		 const void *tgt, int err,
-		 const struct bpf_map *map, u32 index),
-	TP_ARGS(dev, xdp, tgt, err, map, index)
+		 enum bpf_map_type map_type,
+		 u32 map_id, u32 index),
+	TP_ARGS(dev, xdp, tgt, err, map_type, map_id, index)
 );
 
 TRACE_EVENT(xdp_cpumap_kthread,