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, 107 insertions, 0 deletions

diff --git a/include/net/sctp/auth.h b/include/net/sctp/auth.h
new file mode 100644
index 000000000..6f2cd562b
--- /dev/null
+++ b/include/net/sctp/auth.h
@@ -0,0 +1,107 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* SCTP kernel implementation
+ * (C) Copyright 2007 Hewlett-Packard Development Company, L.P.
+ *
+ * This file is part of the SCTP kernel implementation
+ *
+ * Please send any bug reports or fixes you make to the
+ * email address(es):
+ *    lksctp developers <linux-sctp@vger.kernel.org>
+ *
+ * Written or modified by:
+ *   Vlad Yasevich     <vladislav.yasevich@hp.com>
+ */
+
+#ifndef __sctp_auth_h__
+#define __sctp_auth_h__
+
+#include <linux/list.h>
+#include <linux/refcount.h>
+
+struct sctp_endpoint;
+struct sctp_association;
+struct sctp_authkey;
+struct sctp_hmacalgo;
+
+/* Defines an HMAC algorithm supported by SCTP chunk authentication */
+struct sctp_hmac {
+	__u16 hmac_id;		/* one of SCTP_AUTH_HMAC_ID_* */
+	__u16 hmac_len;		/* length of the HMAC value in bytes */
+};
+
+/* This is generic structure that containst authentication bytes used
+ * as keying material.  It's a what is referred to as byte-vector all
+ * over SCTP-AUTH
+ */
+struct sctp_auth_bytes {
+	refcount_t refcnt;
+	__u32 len;
+	__u8  data[];
+};
+
+/* Definition for a shared key, weather endpoint or association */
+struct sctp_shared_key {
+	struct list_head key_list;
+	struct sctp_auth_bytes *key;
+	refcount_t refcnt;
+	__u16 key_id;
+	__u8 deactivated;
+};
+
+#define key_for_each(__key, __list_head) \
+	list_for_each_entry(__key, __list_head, key_list)
+
+#define key_for_each_safe(__key, __tmp, __list_head) \
+	list_for_each_entry_safe(__key, __tmp, __list_head, key_list)
+
+static inline void sctp_auth_key_hold(struct sctp_auth_bytes *key)
+{
+	if (!key)
+		return;
+
+	refcount_inc(&key->refcnt);
+}
+
+void sctp_auth_key_put(struct sctp_auth_bytes *key);
+struct sctp_shared_key *sctp_auth_shkey_create(__u16 key_id, gfp_t gfp);
+void sctp_auth_destroy_keys(struct list_head *keys);
+int sctp_auth_asoc_init_active_key(struct sctp_association *asoc, gfp_t gfp);
+struct sctp_shared_key *sctp_auth_get_shkey(
+				const struct sctp_association *asoc,
+				__u16 key_id);
+int sctp_auth_asoc_copy_shkeys(const struct sctp_endpoint *ep,
+				struct sctp_association *asoc,
+				gfp_t gfp);
+const struct sctp_hmac *sctp_auth_get_hmac(__u16 hmac_id);
+const struct sctp_hmac *
+sctp_auth_asoc_get_hmac(const struct sctp_association *asoc);
+void sctp_auth_asoc_set_default_hmac(struct sctp_association *asoc,
+				     struct sctp_hmac_algo_param *hmacs);
+int sctp_auth_asoc_verify_hmac_id(const struct sctp_association *asoc,
+				    __be16 hmac_id);
+int sctp_auth_send_cid(enum sctp_cid chunk,
+		       const struct sctp_association *asoc);
+int sctp_auth_recv_cid(enum sctp_cid chunk,
+		       const struct sctp_association *asoc);
+void sctp_auth_calculate_hmac(const struct sctp_association *asoc,
+			      struct sk_buff *skb, struct sctp_auth_chunk *auth,
+			      struct sctp_shared_key *ep_key, gfp_t gfp);
+void sctp_auth_shkey_release(struct sctp_shared_key *sh_key);
+void sctp_auth_shkey_hold(struct sctp_shared_key *sh_key);
+
+/* API Helpers */
+int sctp_auth_ep_add_chunkid(struct sctp_endpoint *ep, __u8 chunk_id);
+int sctp_auth_ep_set_hmacs(struct sctp_endpoint *ep,
+			    struct sctp_hmacalgo *hmacs);
+int sctp_auth_set_key(struct sctp_endpoint *ep, struct sctp_association *asoc,
+		      struct sctp_authkey *auth_key);
+int sctp_auth_set_active_key(struct sctp_endpoint *ep,
+			     struct sctp_association *asoc, __u16 key_id);
+int sctp_auth_del_key_id(struct sctp_endpoint *ep,
+			 struct sctp_association *asoc, __u16 key_id);
+int sctp_auth_deact_key_id(struct sctp_endpoint *ep,
+			   struct sctp_association *asoc, __u16 key_id);
+int sctp_auth_init(struct sctp_endpoint *ep, gfp_t gfp);
+void sctp_auth_free(struct sctp_endpoint *ep);
+
+#endif