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