1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright 2014, Michael Ellerman, IBM Corp.
4 */
5
6#include <sched.h>
7#include <signal.h>
8#include <stdio.h>
9#include <stdlib.h>
10#include <sys/mman.h>
11
12#include "ebb.h"
13
14
15/*
16 * Test that tries to trigger CPU_FTR_PMAO_BUG. Which is a hardware defect
17 * where an exception triggers but we context switch before it is delivered and
18 * lose the exception.
19 */
20
21static int test_body(void)
22{
23	int i, orig_period, max_period;
24	struct event event;
25
26	SKIP_IF(!ebb_is_supported());
27
28	/* We use PMC4 to make sure the kernel switches all counters correctly */
29	event_init_named(&event, 0x40002, "instructions");
30	event_leader_ebb_init(&event);
31
32	event.attr.exclude_kernel = 1;
33	event.attr.exclude_hv = 1;
34	event.attr.exclude_idle = 1;
35
36	FAIL_IF(event_open(&event));
37
38	ebb_enable_pmc_counting(4);
39	setup_ebb_handler(standard_ebb_callee);
40	ebb_global_enable();
41	FAIL_IF(ebb_event_enable(&event));
42
43	/*
44	 * We want a low sample period, but we also want to get out of the EBB
45	 * handler without tripping up again.
46	 *
47	 * This value picked after much experimentation.
48	 */
49	orig_period = max_period = sample_period = 400;
50
51	mtspr(SPRN_PMC4, pmc_sample_period(sample_period));
52
53	while (ebb_state.stats.ebb_count < 1000000) {
54		/*
55		 * We are trying to get the EBB exception to race exactly with
56		 * us entering the kernel to do the syscall. We then need the
57		 * kernel to decide our timeslice is up and context switch to
58		 * the other thread. When we come back our EBB will have been
59		 * lost and we'll spin in this while loop forever.
60		 */
61
62		for (i = 0; i < 100000; i++)
63			sched_yield();
64
65		/* Change the sample period slightly to try and hit the race */
66		if (sample_period >= (orig_period + 200))
67			sample_period = orig_period;
68		else
69			sample_period++;
70
71		if (sample_period > max_period)
72			max_period = sample_period;
73	}
74
75	ebb_freeze_pmcs();
76	ebb_global_disable();
77
78	mtspr(SPRN_PMC4, 0xdead);
79
80	dump_summary_ebb_state();
81	dump_ebb_hw_state();
82
83	event_close(&event);
84
85	FAIL_IF(ebb_state.stats.ebb_count == 0);
86
87	/* We vary our sample period so we need extra fudge here */
88	FAIL_IF(!ebb_check_count(4, orig_period, 2 * (max_period - orig_period)));
89
90	return 0;
91}
92
93static int lost_exception(void)
94{
95	return eat_cpu(test_body);
96}
97
98int main(void)
99{
100	test_harness_set_timeout(300);
101	return test_harness(lost_exception, "lost_exception");
102}
103