// 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");
}