diff options
Diffstat (limited to '')
-rw-r--r-- | tools/testing/selftests/powerpc/pmu/ebb/lost_exception_test.c | 102 |
1 files changed, 102 insertions, 0 deletions
diff --git a/tools/testing/selftests/powerpc/pmu/ebb/lost_exception_test.c b/tools/testing/selftests/powerpc/pmu/ebb/lost_exception_test.c new file mode 100644 index 000000000..ba2681a12 --- /dev/null +++ b/tools/testing/selftests/powerpc/pmu/ebb/lost_exception_test.c @@ -0,0 +1,102 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright 2014, Michael Ellerman, IBM Corp. + */ + +#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(); + + 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"); +} |