Commit 4b69e313 authored by Leon Hwang's avatar Leon Hwang Committed by Alexei Starovoitov
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selftests/bpf: Introduce experimental bpf_in_interrupt() 



Filtering pid_tgid is meanlingless when the current task is preempted by
an interrupt.

To address this, introduce 'bpf_in_interrupt()' helper function, which
allows BPF programs to determine whether they are executing in interrupt
context.

'get_preempt_count()':

* On x86, '*(int *) bpf_this_cpu_ptr(&__preempt_count)'.
* On arm64, 'bpf_get_current_task_btf()->thread_info.preempt.count'.

Then 'bpf_in_interrupt()' will be:

* If !PREEMPT_RT, 'get_preempt_count() & (NMI_MASK | HARDIRQ_MASK
  | SOFTIRQ_MASK)'.
* If PREEMPT_RT, '(get_preempt_count() & (NMI_MASK | HARDIRQ_MASK))
  | (bpf_get_current_task_btf()->softirq_disable_cnt & SOFTIRQ_MASK)'.

As for other archs, it can be added support by updating
'get_preempt_count()'.

Suggested-by: default avatarAlexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: default avatarLeon Hwang <leon.hwang@linux.dev>
Link: https://lore.kernel.org/r/20250903140438.59517-2-leon.hwang@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 929adf88

tools/testing/selftests/bpf/bpf_experimental.h

+54 −0
Original line number Diff line number Diff line
@@ -599,4 +599,58 @@ extern void bpf_iter_dmabuf_destroy(struct bpf_iter_dmabuf *it) __weak __ksym; 
extern int bpf_cgroup_read_xattr(struct cgroup *cgroup, const char *name__str,

				 struct bpf_dynptr *value_p) __weak __ksym;



#define PREEMPT_BITS	8

#define SOFTIRQ_BITS	8

#define HARDIRQ_BITS	4

#define NMI_BITS	4



#define PREEMPT_SHIFT	0

#define SOFTIRQ_SHIFT	(PREEMPT_SHIFT + PREEMPT_BITS)

#define HARDIRQ_SHIFT	(SOFTIRQ_SHIFT + SOFTIRQ_BITS)

#define NMI_SHIFT	(HARDIRQ_SHIFT + HARDIRQ_BITS)



#define __IRQ_MASK(x)	((1UL << (x))-1)



#define SOFTIRQ_MASK	(__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)

#define HARDIRQ_MASK	(__IRQ_MASK(HARDIRQ_BITS) << HARDIRQ_SHIFT)

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



extern bool CONFIG_PREEMPT_RT __kconfig __weak;

#ifdef bpf_target_x86

extern const int __preempt_count __ksym;

#endif



struct task_struct___preempt_rt {

	int softirq_disable_cnt;

} __attribute__((preserve_access_index));



static inline int get_preempt_count(void)

{

#if defined(bpf_target_x86)

	return *(int *) bpf_this_cpu_ptr(&__preempt_count);

#elif defined(bpf_target_arm64)

	return bpf_get_current_task_btf()->thread_info.preempt.count;

#endif

	return 0;

}



/* Description

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

 *	* x86

 *	* arm64

 */

static inline int bpf_in_interrupt(void)

{

	struct task_struct___preempt_rt *tsk;

	int pcnt;



	pcnt = get_preempt_count();

	if (!CONFIG_PREEMPT_RT)

		return pcnt & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_MASK);



	tsk = (void *) bpf_get_current_task_btf();

	return (pcnt & (NMI_MASK | HARDIRQ_MASK)) |

	       (tsk->softirq_disable_cnt & SOFTIRQ_MASK);

}



#endif