Commit c31df36b authored by Changwoo Min's avatar Changwoo Min Committed by Alexei Starovoitov
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selftests/bpf: Introduce execution context detection helpers 



Introduce bpf_in_nmi(), bpf_in_hardirq(), bpf_in_serving_softirq(), and
bpf_in_task() inline helpers in bpf_experimental.h. These allow BPF
programs to query the current execution context with higher granularity
than the existing bpf_in_interrupt() helper.

While BPF programs can often infer their context from attachment points,
subsystems like sched_ext may call the same BPF logic from multiple
contexts (e.g., task-to-task wake-ups vs. interrupt-to-task wake-ups).
These helpers provide a reliable way for logic to branch based on
the current CPU execution state.

Implementing these as BPF-native inline helpers wrapping
get_preempt_count() allows the compiler and JIT to inline the logic. The
implementation accounts for differences in preempt_count layout between
standard and PREEMPT_RT kernels.

Reviewed-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarChangwoo Min <changwoo@igalia.com>
Link: https://lore.kernel.org/r/20260125115413.117502-2-changwoo@igalia.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent c390adfd

tools/testing/selftests/bpf/bpf_experimental.h

+58 −0
Original line number Diff line number Diff line
@@ -610,6 +610,8 @@ extern int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__str, 
#define HARDIRQ_MASK	(__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)

#define NMI_MASK	(__IRQ_MASK(NMI_BITS)     << NMI_SHIFT)



#define SOFTIRQ_OFFSET	(1UL << SOFTIRQ_SHIFT)



extern bool CONFIG_PREEMPT_RT __kconfig __weak;

#ifdef bpf_target_x86

extern const int __preempt_count __ksym;
@@ -648,4 +650,60 @@ static inline int bpf_in_interrupt(void) 
	       (tsk->softirq_disable_cnt & SOFTIRQ_MASK);

}



/* Description

 *	Report whether it is in NMI context. Only works on the following archs:

 *	* x86

 *	* arm64

 */

static inline int bpf_in_nmi(void)

{

	return get_preempt_count() & NMI_MASK;

}



/* Description

 *	Report whether it is in hard IRQ context. Only works on the following archs:

 *	* x86

 *	* arm64

 */

static inline int bpf_in_hardirq(void)

{

	return get_preempt_count() & HARDIRQ_MASK;

}



/* Description

 *	Report whether it is in softirq context. Only works on the following archs:

 *	* x86

 *	* arm64

 */

static inline int bpf_in_serving_softirq(void)

{

	struct task_struct___preempt_rt *tsk;

	int pcnt;



	pcnt = get_preempt_count();

	if (!CONFIG_PREEMPT_RT)

		return (pcnt & SOFTIRQ_MASK) & SOFTIRQ_OFFSET;



	tsk = (void *) bpf_get_current_task_btf();

	return (tsk->softirq_disable_cnt & SOFTIRQ_MASK) & SOFTIRQ_OFFSET;

}



/* Description

 *	Report whether it is in task context. Only works on the following archs:

 *	* x86

 *	* arm64

 */

static inline int bpf_in_task(void)

{

	struct task_struct___preempt_rt *tsk;

	int pcnt;



	pcnt = get_preempt_count();

	if (!CONFIG_PREEMPT_RT)

		return !(pcnt & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));



	tsk = (void *) bpf_get_current_task_btf();

	return !((pcnt & (NMI_MASK | HARDIRQ_MASK)) |

		 ((tsk->softirq_disable_cnt & SOFTIRQ_MASK) & SOFTIRQ_OFFSET));

}

#endif