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 #include <time.h> 12 13 #include "ebb.h" 14 15 16 /* 17 * Test that tries to trigger CPU_FTR_PMAO_BUG. Which is a hardware defect 18 * where an exception triggers but we context switch before it is delivered and 19 * lose the exception. 20 */ 21 22 static int test_body(void) 23 { 24 int i, orig_period, max_period; 25 struct event event; 26 struct timespec ts = { .tv_sec = 0, .tv_nsec = 1 }; 27 28 SKIP_IF(!ebb_is_supported()); 29 30 /* We use PMC4 to make sure the kernel switches all counters correctly */ 31 event_init_named(&event, 0x40002, "instructions"); 32 event_leader_ebb_init(&event); 33 34 event.attr.exclude_kernel = 1; 35 event.attr.exclude_hv = 1; 36 event.attr.exclude_idle = 1; 37 38 FAIL_IF(event_open(&event)); 39 40 ebb_enable_pmc_counting(4); 41 setup_ebb_handler(standard_ebb_callee); 42 ebb_global_enable(); 43 FAIL_IF(ebb_event_enable(&event)); 44 45 /* 46 * We want a low sample period, but we also want to get out of the EBB 47 * handler without tripping up again. 48 * 49 * This value picked after much experimentation. 50 */ 51 orig_period = max_period = sample_period = 400; 52 53 mtspr(SPRN_PMC4, pmc_sample_period(sample_period)); 54 55 while (ebb_state.stats.ebb_count < 1000000) { 56 /* 57 * We are trying to get the EBB exception to race exactly with 58 * us entering the kernel to do the syscall. We then need the 59 * kernel to decide our timeslice is up and context switch to 60 * the other thread. When we come back our EBB will have been 61 * lost and we'll spin in this while loop forever. 62 * 63 * Use nanosleep(0) instead of sched_yield() to guarantee a 64 * context switch to the eat_cpu child regardless of the 65 * eligibility state. sched_yield() via yield_task_fair() may 66 * become a no-op when the task is ineligible (vruntime ahead 67 * of avg_vruntime), preventing the required context switch. 68 */ 69 for (i = 0; i < 100000; i++) 70 nanosleep(&ts, NULL); 71 72 /* Change the sample period slightly to try and hit the race */ 73 if (sample_period >= (orig_period + 200)) 74 sample_period = orig_period; 75 else 76 sample_period++; 77 78 if (sample_period > max_period) 79 max_period = sample_period; 80 } 81 82 ebb_freeze_pmcs(); 83 ebb_global_disable(); 84 85 mtspr(SPRN_PMC4, 0xdead); 86 87 dump_summary_ebb_state(); 88 dump_ebb_hw_state(); 89 90 event_close(&event); 91 92 FAIL_IF(ebb_state.stats.ebb_count == 0); 93 94 /* We vary our sample period so we need extra fudge here */ 95 FAIL_IF(!ebb_check_count(4, orig_period, 2 * (max_period - orig_period))); 96 97 return 0; 98 } 99 100 static int lost_exception(void) 101 { 102 return eat_cpu(test_body); 103 } 104 105 int main(void) 106 { 107 test_harness_set_timeout(300); 108 return test_harness(lost_exception, "lost_exception"); 109 } 110