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/*
* 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;
/* 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)
{
return test_harness(lost_exception, "lost_exception");
}
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