sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 230 insertions, 0 deletions

diff --git a/include/net/fib_rules.h b/include/net/fib_rules.h
new file mode 100644
index 000000000..7dee0ae61
--- /dev/null
+++ b/include/net/fib_rules.h
@@ -0,0 +1,230 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __NET_FIB_RULES_H
+#define __NET_FIB_RULES_H
+
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/netdevice.h>
+#include <linux/fib_rules.h>
+#include <linux/refcount.h>
+#include <net/flow.h>
+#include <net/rtnetlink.h>
+#include <net/fib_notifier.h>
+#include <linux/indirect_call_wrapper.h>
+
+struct fib_kuid_range {
+	kuid_t start;
+	kuid_t end;
+};
+
+struct fib_rule {
+	struct list_head	list;
+	int			iifindex;
+	int			oifindex;
+	u32			mark;
+	u32			mark_mask;
+	u32			flags;
+	u32			table;
+	u8			action;
+	u8			l3mdev;
+	u8                      proto;
+	u8			ip_proto;
+	u32			target;
+	__be64			tun_id;
+	struct fib_rule __rcu	*ctarget;
+	struct net		*fr_net;
+
+	refcount_t		refcnt;
+	u32			pref;
+	int			suppress_ifgroup;
+	int			suppress_prefixlen;
+	char			iifname[IFNAMSIZ];
+	char			oifname[IFNAMSIZ];
+	struct fib_kuid_range	uid_range;
+	struct fib_rule_port_range	sport_range;
+	struct fib_rule_port_range	dport_range;
+	u16			sport_mask;
+	u16			dport_mask;
+	u8                      iif_is_l3_master;
+	u8                      oif_is_l3_master;
+	struct rcu_head		rcu;
+};
+
+struct fib_lookup_arg {
+	void			*lookup_ptr;
+	const void		*lookup_data;
+	void			*result;
+	struct fib_rule		*rule;
+	u32			table;
+	int			flags;
+#define FIB_LOOKUP_NOREF		1
+#define FIB_LOOKUP_IGNORE_LINKSTATE	2
+};
+
+struct fib_rules_ops {
+	int			family;
+	struct list_head	list;
+	int			rule_size;
+	int			addr_size;
+	int			unresolved_rules;
+	int			nr_goto_rules;
+	unsigned int		fib_rules_seq;
+
+	int			(*action)(struct fib_rule *,
+					  struct flowi *, int,
+					  struct fib_lookup_arg *);
+	bool			(*suppress)(struct fib_rule *, int,
+					    struct fib_lookup_arg *);
+	int			(*match)(struct fib_rule *,
+					 struct flowi *, int);
+	int			(*configure)(struct fib_rule *,
+					     struct sk_buff *,
+					     struct fib_rule_hdr *,
+					     struct nlattr **,
+					     struct netlink_ext_ack *);
+	int			(*delete)(struct fib_rule *);
+	int			(*compare)(struct fib_rule *,
+					   struct fib_rule_hdr *,
+					   struct nlattr **);
+	int			(*fill)(struct fib_rule *, struct sk_buff *,
+					struct fib_rule_hdr *);
+	size_t			(*nlmsg_payload)(struct fib_rule *);
+
+	/* Called after modifications to the rules set, must flush
+	 * the route cache if one exists. */
+	void			(*flush_cache)(struct fib_rules_ops *ops);
+
+	int			nlgroup;
+	struct list_head	rules_list;
+	struct module		*owner;
+	struct net		*fro_net;
+	struct rcu_head		rcu;
+};
+
+struct fib_rule_notifier_info {
+	struct fib_notifier_info info; /* must be first */
+	struct fib_rule *rule;
+};
+
+static inline void fib_rule_get(struct fib_rule *rule)
+{
+	refcount_inc(&rule->refcnt);
+}
+
+static inline bool fib_rule_get_safe(struct fib_rule *rule)
+{
+	return refcount_inc_not_zero(&rule->refcnt);
+}
+
+static inline void fib_rule_put(struct fib_rule *rule)
+{
+	if (refcount_dec_and_test(&rule->refcnt))
+		kfree_rcu(rule, rcu);
+}
+
+#ifdef CONFIG_NET_L3_MASTER_DEV
+static inline u32 fib_rule_get_table(struct fib_rule *rule,
+				     struct fib_lookup_arg *arg)
+{
+	return rule->l3mdev ? arg->table : rule->table;
+}
+#else
+static inline u32 fib_rule_get_table(struct fib_rule *rule,
+				     struct fib_lookup_arg *arg)
+{
+	return rule->table;
+}
+#endif
+
+static inline u32 frh_get_table(struct fib_rule_hdr *frh, struct nlattr **nla)
+{
+	if (nla[FRA_TABLE])
+		return nla_get_u32(nla[FRA_TABLE]);
+	return frh->table;
+}
+
+static inline bool fib_rule_port_range_set(const struct fib_rule_port_range *range)
+{
+	return range->start != 0 && range->end != 0;
+}
+
+static inline bool fib_rule_port_inrange(const struct fib_rule_port_range *a,
+					 __be16 port)
+{
+	return ntohs(port) >= a->start &&
+		ntohs(port) <= a->end;
+}
+
+static inline bool fib_rule_port_match(const struct fib_rule_port_range *range,
+				       u16 port_mask, __be16 port)
+{
+	if ((range->start ^ ntohs(port)) & port_mask)
+		return false;
+	if (!port_mask && fib_rule_port_range_set(range) &&
+	    !fib_rule_port_inrange(range, port))
+		return false;
+	return true;
+}
+
+static inline bool fib_rule_port_range_valid(const struct fib_rule_port_range *a)
+{
+	return a->start != 0 && a->end != 0 && a->end < 0xffff &&
+		a->start <= a->end;
+}
+
+static inline bool fib_rule_port_range_compare(struct fib_rule_port_range *a,
+					       struct fib_rule_port_range *b)
+{
+	return a->start == b->start &&
+		a->end == b->end;
+}
+
+static inline bool
+fib_rule_port_is_range(const struct fib_rule_port_range *range)
+{
+	return range->start != range->end;
+}
+
+static inline bool fib_rule_requires_fldissect(struct fib_rule *rule)
+{
+	return rule->iifindex != LOOPBACK_IFINDEX && (rule->ip_proto ||
+		fib_rule_port_range_set(&rule->sport_range) ||
+		fib_rule_port_range_set(&rule->dport_range));
+}
+
+struct fib_rules_ops *fib_rules_register(const struct fib_rules_ops *,
+					 struct net *);
+void fib_rules_unregister(struct fib_rules_ops *);
+
+int fib_rules_lookup(struct fib_rules_ops *, struct flowi *, int flags,
+		     struct fib_lookup_arg *);
+int fib_default_rule_add(struct fib_rules_ops *, u32 pref, u32 table);
+bool fib_rule_matchall(const struct fib_rule *rule);
+int fib_rules_dump(struct net *net, struct notifier_block *nb, int family,
+		   struct netlink_ext_ack *extack);
+unsigned int fib_rules_seq_read(const struct net *net, int family);
+
+int fib_newrule(struct net *net, struct sk_buff *skb, struct nlmsghdr *nlh,
+		struct netlink_ext_ack *extack, bool rtnl_held);
+int fib_delrule(struct net *net, struct sk_buff *skb, struct nlmsghdr *nlh,
+		struct netlink_ext_ack *extack, bool rtnl_held);
+
+INDIRECT_CALLABLE_DECLARE(int fib6_rule_match(struct fib_rule *rule,
+					    struct flowi *fl, int flags));
+INDIRECT_CALLABLE_DECLARE(int fib4_rule_match(struct fib_rule *rule,
+					    struct flowi *fl, int flags));
+
+INDIRECT_CALLABLE_DECLARE(int fib6_rule_action(struct fib_rule *rule,
+			    struct flowi *flp, int flags,
+			    struct fib_lookup_arg *arg));
+INDIRECT_CALLABLE_DECLARE(int fib4_rule_action(struct fib_rule *rule,
+			    struct flowi *flp, int flags,
+			    struct fib_lookup_arg *arg));
+
+INDIRECT_CALLABLE_DECLARE(bool fib6_rule_suppress(struct fib_rule *rule,
+						int flags,
+						struct fib_lookup_arg *arg));
+INDIRECT_CALLABLE_DECLARE(bool fib4_rule_suppress(struct fib_rule *rule,
+						int flags,
+						struct fib_lookup_arg *arg));
+#endif