tools/testing/selftests/powerpc/pmu/ebb/lost_exception_test.c

   1 /*
   2  * Copyright 2014, Michael Ellerman, IBM Corp.
   3  * Licensed under GPLv2.
   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 defect
  17  * where an exception triggers but we context switch before it is delivered and
  18  * lose the exception.
  19  */
  20
  21 static 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 EBB
  45          * 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 with
  56                  * us entering the kernel to do the syscall. We then need the
  57                  * kernel to decide our timeslice is up and context switch to
  58                  * the other thread. When we come back our EBB will have been
  59                  * 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                 else
  69                         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         count_pmc(4, sample_period);
  79         mtspr(SPRN_PMC4, 0xdead);
  80
  81         dump_summary_ebb_state();
  82         dump_ebb_hw_state();
  83
  84         event_close(&event);
  85
  86         FAIL_IF(ebb_state.stats.ebb_count == 0);
  87
  88         /* We vary our sample period so we need extra fudge here */
  89         FAIL_IF(!ebb_check_count(4, orig_period, 2 * (max_period - orig_period)));
  90
  91         return 0;
  92 }
  93
  94 static int lost_exception(void)
  95 {
  96         return eat_cpu(test_body);
  97 }
  98
  99 int main(void)
 100 {
 101         return test_harness(lost_exception, "lost_exception");
 102 }