103 lines · c
1// SPDX-License-Identifier: GPL-2.0-only2/*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 defect17 * where an exception triggers but we context switch before it is delivered and18 * lose the exception.19 */20 21static 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 EBB45 * 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 with56 * us entering the kernel to do the syscall. We then need the57 * kernel to decide our timeslice is up and context switch to58 * the other thread. When we come back our EBB will have been59 * 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 else69 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 93static int lost_exception(void)94{95 return eat_cpu(test_body);96}97 98int main(void)99{100 test_harness_set_timeout(300);101 return test_harness(lost_exception, "lost_exception");102}103