Re: [PATCH v2 bpf-next 2/5] bpf: Add support to attach bpf program to a devmap entry

From: David Ahern <redacted>

Add BPF_XDP_DEVMAP attach type for use with programs associated with a
DEVMAP entry.

Allow DEVMAPs to associate a program with a device entry by adding
a bpf_prog_fd to 'struct devmap_val'. Values read show the program
id, so the fd and id are a union.

The program associated with the fd must have type XDP with expected
attach type BPF_XDP_DEVMAP. When a program is associated with a device
index, the program is run on an XDP_REDIRECT and before the buffer is
added to the per-cpu queue. At this point rxq data is still valid; the
next patch adds tx device information allowing the prorgam to see both
ingress and egress device indices.

XDP generic is skb based and XDP programs do not work with skb's. Block
the use case by walking maps used by a program that is to be attached
via xdpgeneric and fail if any of them are DEVMAP / DEVMAP_HASH with
 > 4-byte values.

Block attach of BPF_XDP_DEVMAP programs to devices.

Signed-off-by: David Ahern <redacted>
---
 include/linux/bpf.h            |  5 +++
 include/uapi/linux/bpf.h       |  5 +++
 kernel/bpf/devmap.c            | 79 +++++++++++++++++++++++++++++++++-
 net/core/dev.c                 | 18 ++++++++
 tools/include/uapi/linux/bpf.h |  5 +++
 5 files changed, 110 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index efe8836b5c48..088751bc09aa 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -1242,6 +1242,7 @@ int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_buff *xdp,
 		    struct net_device *dev_rx);
 int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
 			     struct bpf_prog *xdp_prog);
+bool dev_map_can_have_prog(struct bpf_map *map);
 
 struct bpf_cpu_map_entry *__cpu_map_lookup_elem(struct bpf_map *map, u32 key);
 void __cpu_map_flush(void);

@@ -1355,6 +1356,10 @@ static inline struct net_device  *__dev_map_hash_lookup_elem(struct bpf_map *map
 {
 	return NULL;
 }
+static inline bool dev_map_can_have_prog(struct bpf_map *map)
+{
+	return false;
+}
 
 static inline void __dev_flush(void)
 {

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index d27302ecaa9c..2d9927b7a922 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -224,6 +224,7 @@ enum bpf_attach_type {
 	BPF_CGROUP_INET6_GETPEERNAME,
 	BPF_CGROUP_INET4_GETSOCKNAME,
 	BPF_CGROUP_INET6_GETSOCKNAME,
+	BPF_XDP_DEVMAP,
 	__MAX_BPF_ATTACH_TYPE
 };
 

@@ -3628,6 +3629,10 @@ struct xdp_md {
 /* DEVMAP values */
 struct devmap_val {
 	__u32 ifindex;   /* device index */
+	union {
+		int   bpf_prog_fd;  /* prog fd on map write */
+		__u32 bpf_prog_id;  /* prog id on map read */
+	};
 };
 
 enum sk_action {

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 069a50113e26..a628585a31e1 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c

@@ -64,6 +64,7 @@ struct bpf_dtab_netdev {
 	struct net_device *dev; /* must be first member, due to tracepoint */
 	struct hlist_node index_hlist;
 	struct bpf_dtab *dtab;
+	struct bpf_prog *xdp_prog;
 	struct rcu_head rcu;
 	unsigned int idx;
 	struct devmap_val val;

@@ -219,6 +220,8 @@ static void dev_map_free(struct bpf_map *map)
 
 			hlist_for_each_entry_safe(dev, next, head, index_hlist) {
 				hlist_del_rcu(&dev->index_hlist);
+				if (dev->xdp_prog)
+					bpf_prog_put(dev->xdp_prog);
 				dev_put(dev->dev);
 				kfree(dev);
 			}

@@ -233,6 +236,8 @@ static void dev_map_free(struct bpf_map *map)
 			if (!dev)
 				continue;
 
+			if (dev->xdp_prog)
+				bpf_prog_put(dev->xdp_prog);
 			dev_put(dev->dev);
 			kfree(dev);
 		}

@@ -319,6 +324,16 @@ static int dev_map_hash_get_next_key(struct bpf_map *map, void *key,
 	return -ENOENT;
 }
 
+bool dev_map_can_have_prog(struct bpf_map *map)
+{
+	if ((map->map_type == BPF_MAP_TYPE_DEVMAP ||
+	     map->map_type == BPF_MAP_TYPE_DEVMAP_HASH) &&
+	    map->value_size != 4)