arch/x86/kernel/tracepoint.c

   1 /*
   2  * Code for supporting irq vector tracepoints.
   3  *
   4  * Copyright (C) 2013 Seiji Aguchi <seiji.aguchi@hds.com>
   5  *
   6  */
   7 #include <asm/hw_irq.h>
   8 #include <asm/desc.h>
   9 #include <linux/atomic.h>
  10
  11 atomic_t trace_idt_ctr = ATOMIC_INIT(0);
  12 struct desc_ptr trace_idt_descr = { NR_VECTORS * 16 - 1,
  13                                 (unsigned long) trace_idt_table };
  14
  15 /* No need to be aligned, but done to keep all IDTs defined the same way. */
  16 gate_desc trace_idt_table[NR_VECTORS] __page_aligned_bss;
  17
  18 static int trace_irq_vector_refcount;
  19 static DEFINE_MUTEX(irq_vector_mutex);
  20
  21 static void set_trace_idt_ctr(int val)
  22 {
  23         atomic_set(&trace_idt_ctr, val);
  24         /* Ensure the trace_idt_ctr is set before sending IPI */
  25         wmb();
  26 }
  27
  28 static void switch_idt(void *arg)
  29 {
  30         unsigned long flags;
  31
  32         local_irq_save(flags);
  33         load_current_idt();
  34         local_irq_restore(flags);
  35 }
  36
  37 int trace_irq_vector_regfunc(void)
  38 {
  39         mutex_lock(&irq_vector_mutex);
  40         if (!trace_irq_vector_refcount) {
  41                 set_trace_idt_ctr(1);
  42                 smp_call_function(switch_idt, NULL, 0);
  43                 switch_idt(NULL);
  44         }
  45         trace_irq_vector_refcount++;
  46         mutex_unlock(&irq_vector_mutex);
  47         return 0;
  48 }
  49
  50 void trace_irq_vector_unregfunc(void)
  51 {
  52         mutex_lock(&irq_vector_mutex);
  53         trace_irq_vector_refcount--;
  54         if (!trace_irq_vector_refcount) {
  55                 set_trace_idt_ctr(0);
  56                 smp_call_function(switch_idt, NULL, 0);
  57                 switch_idt(NULL);
  58         }
  59         mutex_unlock(&irq_vector_mutex);
  60 }