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
21 static 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
93 static int lost_exception(void)
94 {
95 return eat_cpu(test_body);
96 }
97
98 int main(void)
99 {
100 test_harness_set_timeout(300);
101 return test_harness(lost_exception, "lost_exception");
102 }
103
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