linux-kernel - [PATCH bpf-next v1 1/2] bpf: Introduce execution context detection kfuncs

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Message-ID: <20260123084248.259278-2-changwoo@igalia.com>
Date: Fri, 23 Jan 2026 17:42:47 +0900
From: Changwoo Min <changwoo@...lia.com>
To: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Shuah Khan <shuah@...nel.org>,
	kernel-dev@...lia.com,
	bpf@...r.kernel.org,
	sched-ext@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	Changwoo Min <changwoo@...lia.com>
Subject: [PATCH bpf-next v1 1/2] bpf: Introduce execution context detection kfuncs

Introduce bpf_in_nmi(), bpf_in_hardirq(), bpf_in_serving_softirq(), and
bpf_in_task() kfuncs to allow BPF programs to query the current execution
context.

While BPF programs can sometimes infer context based on the attach point,
certain programs (such as those in sched_ext) may be called from multiple
contexts. These kfuncs provide a reliable way for logic to branch based on
whether the CPU is currently handling an interrupt or executing in task
context.

For example, this is particularly useful for sched_ext schedulers that need
to differentiate between task-to-task wake-ups and interrupt-to-task
wake-ups.

As the names imply, these helpers wrap the kernel's internal in_nmi(),
in_hardirq(), in_serving_softirq(), and in_task() macros.

Signed-off-by: Changwoo Min <changwoo@...lia.com>
---
 kernel/bpf/helpers.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 637677815365..cb36bc7a80c6 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -4365,6 +4365,46 @@ __bpf_kfunc int bpf_dynptr_file_discard(struct bpf_dynptr *dynptr)
 	return 0;
 }
 
+/**
+ * bpf_in_nmi - Test if the current execution context is in NMI context.
+ *
+ * Return: true if we are in NMI context, false otherwise.
+ */
+__bpf_kfunc bool bpf_in_nmi(void)
+{
+	return in_nmi();
+}
+
+/**
+ * bpf_in_hardirq - Test if the current execution context is in hard IRQ context.
+ *
+ * Return: true if we are in hard IRQ context, false otherwise.
+ */
+__bpf_kfunc bool bpf_in_hardirq(void)
+{
+	return in_hardirq();
+}
+
+/**
+ * bpf_in_serving_softirq - Test if the current execution context is in softirq context.
+ *
+ * Return: true if we are in softirq context, false otherwise.
+ */
+__bpf_kfunc bool bpf_in_serving_softirq(void)
+{
+	return in_serving_softirq();
+}
+
+/**
+ * bpf_in_task - Test if the current execution context is in task context.
+ *
+ * Return: true if we are in task context, false otherwise.
+ */
+__bpf_kfunc bool bpf_in_task(void)
+{
+	return in_task();
+}
+
 __bpf_kfunc_end_defs();
 
 static void bpf_task_work_cancel_scheduled(struct irq_work *irq_work)
@@ -4546,6 +4586,10 @@ BTF_ID_FLAGS(func, bpf_task_work_schedule_signal, KF_IMPLICIT_ARGS)
 BTF_ID_FLAGS(func, bpf_task_work_schedule_resume, KF_IMPLICIT_ARGS)
 BTF_ID_FLAGS(func, bpf_dynptr_from_file)
 BTF_ID_FLAGS(func, bpf_dynptr_file_discard)
+BTF_ID_FLAGS(func, bpf_in_nmi)
+BTF_ID_FLAGS(func, bpf_in_hardirq)
+BTF_ID_FLAGS(func, bpf_in_serving_softirq)
+BTF_ID_FLAGS(func, bpf_in_task)
 BTF_KFUNCS_END(common_btf_ids)
 
 static const struct btf_kfunc_id_set common_kfunc_set = {
-- 
2.52.0