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selftests/bpf: Introduce execution context detection helpers

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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: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Changwoo Min <changwoo@igalia.com>
Link: https://lore.kernel.org/r/20260125115413.117502-2-changwoo@igalia.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Changwoo Min 2026-01-25 20:54:12 +09:00 committed by Alexei Starovoitov
parent c390adfda2
commit c31df36bd2
1 changed files with 58 additions and 0 deletions
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58
tools/testing/selftests/bpf/bpf_experimental.h
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@ -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