kernel/critical.c

   1 #include "critical.h"
   2 #include "stddef.h"
   3 #include "stdint.h"
   4 #include "general.h"
   5 #include "mp_tables.h"
   6 #include "cpuid.h"
   7
   8 static struct mp_counts mp;
   9 static volatile uint32_t spinlock = 0;     /* volatile to not optimize the smp_lock loop away */
  10
  11 // defined in criticala.asm
  12 int critical_enter_internal(void);
  13
  14 static void smp_lock(void)
  15 {
  16     memory_barrier();               /* syncronize */
  17     asm volatile(
  18         "1:                         "
  19         "    pause;                 " /* used to optimize loops on P4/Xeon's */
  20         "    lock btsl $0x00, %0;   " /* if no lock is set, it will btsl (bit set long) */
  21         "    jc 1b;                 " /* still locked? */
  22         ::"m"(spinlock)
  23         : "cc");
  24 }
  25
  26 static void smp_unlock(void)
  27 {
  28     spinlock = 0;       /* unlock */
  29 }
  30
  31 int critical_enter(void)
  32 {
  33     int state = critical_enter_internal();
  34     if (state == 1){
  35         // interrupts *were* enabled
  36         if(mp.processor_count > 1)
  37         {
  38             smp_lock();
  39         }
  40     }
  41     return state;
  42 }
  43
  44 void critical_exit(int state)
  45 {
  46     if (state == 1){
  47         if(mp.processor_count > 1){
  48             smp_unlock();
  49         }
  50         sti();
  51     }
  52 }
  53
  54 /* mb = memory barrier, used for code synchronization */
  55 void memory_barrier(void)
  56 {
  57     if(cpuid.features_edx & (1 << 26)) /* test for SSE2 */
  58     {
  59         asm volatile("mfence");
  60     }
  61 }
  62