[PATCH bpf-next v4 3/7] bpf: Add kfunc bpf_rcu_read_lock/unlock()

[Yonghong Song <yhs@fb.com>]

Add two kfunc's bpf_rcu_read_lock() and bpf_rcu_read_unlock(). These two kfunc's
can be used for all program types. A new kfunc hook type BTF_KFUNC_HOOK_GENERIC
is added which corresponds to prog type BPF_PROG_TYPE_UNSPEC, indicating the
kfunc intends to be used for all prog types.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
 include/linux/bpf.h  |  3 +++
 kernel/bpf/btf.c     |  8 ++++++++
 kernel/bpf/helpers.c | 25 ++++++++++++++++++++++++-
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 798aec816970..3ed817cf191d 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2113,6 +2113,9 @@ bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog);
 const struct btf_func_model *
 bpf_jit_find_kfunc_model(const struct bpf_prog *prog,
 			 const struct bpf_insn *insn);
+void bpf_rcu_read_lock(void);
+void bpf_rcu_read_unlock(void);
+
 struct bpf_core_ctx {
 	struct bpf_verifier_log *log;
 	const struct btf *btf;
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 5579ff3a5b54..84f09235857c 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -199,6 +199,7 @@ DEFINE_IDR(btf_idr);
 DEFINE_SPINLOCK(btf_idr_lock);
 
 enum btf_kfunc_hook {
+	BTF_KFUNC_HOOK_GENERIC,
 	BTF_KFUNC_HOOK_XDP,
 	BTF_KFUNC_HOOK_TC,
 	BTF_KFUNC_HOOK_STRUCT_OPS,
@@ -7499,6 +7500,8 @@ static u32 *__btf_kfunc_id_set_contains(const struct btf *btf,
 static int bpf_prog_type_to_kfunc_hook(enum bpf_prog_type prog_type)
 {
 	switch (prog_type) {
+	case BPF_PROG_TYPE_UNSPEC:
+		return BTF_KFUNC_HOOK_GENERIC;
 	case BPF_PROG_TYPE_XDP:
 		return BTF_KFUNC_HOOK_XDP;
 	case BPF_PROG_TYPE_SCHED_CLS:
@@ -7527,6 +7530,11 @@ u32 *btf_kfunc_id_set_contains(const struct btf *btf,
 			       u32 kfunc_btf_id)
 {
 	enum btf_kfunc_hook hook;
+	u32 *kfunc_flags;
+
+	kfunc_flags = __btf_kfunc_id_set_contains(btf, BTF_KFUNC_HOOK_GENERIC, kfunc_btf_id);
+	if (kfunc_flags)
+		return kfunc_flags;
 
 	hook = bpf_prog_type_to_kfunc_hook(prog_type);
 	return __btf_kfunc_id_set_contains(btf, hook, kfunc_btf_id);
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 283f55bbeb70..0c8382103625 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -1717,9 +1717,32 @@ static const struct btf_kfunc_id_set tracing_kfunc_set = {
 	.set   = &tracing_btf_ids,
 };
 
+void bpf_rcu_read_lock(void)
+{
+	rcu_read_lock();
+}
+
+void bpf_rcu_read_unlock(void)
+{
+	rcu_read_unlock();
+}
+
+BTF_SET8_START(generic_btf_ids)
+BTF_ID_FLAGS(func, bpf_rcu_read_lock)
+BTF_ID_FLAGS(func, bpf_rcu_read_unlock)
+BTF_SET8_END(generic_btf_ids)
+
+static const struct btf_kfunc_id_set generic_kfunc_set = {
+	.owner = THIS_MODULE,
+	.set   = &generic_btf_ids,
+};
+
 static int __init kfunc_init(void)
 {
-	return register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &tracing_kfunc_set);
+	int ret;
+
+	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &tracing_kfunc_set);
+	return ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC, &generic_kfunc_set);
 }
 
 late_initcall(kfunc_init);
-- 
2.30.2