/* * Copyright 2014, Michael Ellerman, IBM Corp. * Licensed under GPLv2. */ #include <sched.h> #include <signal.h> #include <stdio.h> #include <stdlib.h> #include <sys/mman.h> #include "ebb.h" /* * Test that tries to trigger CPU_FTR_PMAO_BUG. Which is a hardware defect * where an exception triggers but we context switch before it is delivered and * lose the exception. */ static int test_body(void) { int i, orig_period, max_period; struct event event; SKIP_IF(!ebb_is_supported()); /* We use PMC4 to make sure the kernel switches all counters correctly */ event_init_named(&event, 0x40002, "instructions"); event_leader_ebb_init(&event); event.attr.exclude_kernel = 1; event.attr.exclude_hv = 1; event.attr.exclude_idle = 1; FAIL_IF(event_open(&event)); ebb_enable_pmc_counting(4); setup_ebb_handler(standard_ebb_callee); ebb_global_enable(); FAIL_IF(ebb_event_enable(&event)); /* * We want a low sample period, but we also want to get out of the EBB * handler without tripping up again. * * This value picked after much experimentation. */ orig_period = max_period = sample_period = 400; mtspr(SPRN_PMC4, pmc_sample_period(sample_period)); while (ebb_state.stats.ebb_count < 1000000) { /* * We are trying to get the EBB exception to race exactly with * us entering the kernel to do the syscall. We then need the * kernel to decide our timeslice is up and context switch to * the other thread. When we come back our EBB will have been * lost and we'll spin in this while loop forever. */ for (i = 0; i < 100000; i++) sched_yield(); /* Change the sample period slightly to try and hit the race */ if (sample_period >= (orig_period + 200)) sample_period = orig_period; else sample_period++; if (sample_period > max_period) max_period = sample_period; } ebb_freeze_pmcs(); ebb_global_disable(); count_pmc(4, sample_period); mtspr(SPRN_PMC4, 0xdead); dump_summary_ebb_state(); dump_ebb_hw_state(); event_close(&event); FAIL_IF(ebb_state.stats.ebb_count == 0); /* We vary our sample period so we need extra fudge here */ FAIL_IF(!ebb_check_count(4, orig_period, 2 * (max_period - orig_period))); return 0; } static int lost_exception(void) { return eat_cpu(test_body); } int main(void) { test_harness_set_timeout(300); return test_harness(lost_exception, "lost_exception"); }