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 <stdbool.h>
9 #include <stdio.h>
10 #include <stdlib.h>
11
12 #include "ebb.h"
13
14
15 /*
16 * Test that the kernel properly handles PMAE across context switches.
17 *
18 * We test this by calling into the kernel inside our EBB handler, where PMAE
19 * is clear. A cpu eater companion thread is running on the same CPU as us to
20 * encourage the scheduler to switch us.
21 *
22 * The kernel must make sure that when it context switches us back in, it
23 * honours the fact that we had PMAE clear.
24 *
25 * Observed to hit the failing case on the first EBB with a broken kernel.
26 */
27
28 static bool mmcr0_mismatch;
29 static uint64_t before, after;
30
syscall_ebb_callee(void)31 static void syscall_ebb_callee(void)
32 {
33 uint64_t val;
34
35 val = mfspr(SPRN_BESCR);
36 if (!(val & BESCR_PMEO)) {
37 ebb_state.stats.spurious++;
38 goto out;
39 }
40
41 ebb_state.stats.ebb_count++;
42 count_pmc(1, sample_period);
43
44 before = mfspr(SPRN_MMCR0);
45
46 /* Try and get ourselves scheduled, to force a PMU context switch */
47 sched_yield();
48
49 after = mfspr(SPRN_MMCR0);
50 if (before != after)
51 mmcr0_mismatch = true;
52
53 out:
54 reset_ebb();
55 }
56
test_body(void)57 static int test_body(void)
58 {
59 struct event event;
60
61 SKIP_IF(!ebb_is_supported());
62
63 event_init_named(&event, 0x1001e, "cycles");
64 event_leader_ebb_init(&event);
65
66 event.attr.exclude_kernel = 1;
67 event.attr.exclude_hv = 1;
68 event.attr.exclude_idle = 1;
69
70 FAIL_IF(event_open(&event));
71
72 setup_ebb_handler(syscall_ebb_callee);
73 ebb_global_enable();
74
75 FAIL_IF(ebb_event_enable(&event));
76
77 mtspr(SPRN_PMC1, pmc_sample_period(sample_period));
78
79 while (ebb_state.stats.ebb_count < 20 && !mmcr0_mismatch)
80 FAIL_IF(core_busy_loop());
81
82 ebb_global_disable();
83 ebb_freeze_pmcs();
84
85 dump_ebb_state();
86
87 if (mmcr0_mismatch)
88 printf("Saw MMCR0 before 0x%lx after 0x%lx\n", before, after);
89
90 event_close(&event);
91
92 FAIL_IF(ebb_state.stats.ebb_count == 0);
93 FAIL_IF(mmcr0_mismatch);
94
95 return 0;
96 }
97
pmae_handling(void)98 int pmae_handling(void)
99 {
100 return eat_cpu(test_body);
101 }
102
main(void)103 int main(void)
104 {
105 return test_harness(pmae_handling, "pmae_handling");
106 }
107