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