arch/x86/include/asm/barrier.h

   1 #ifndef _ASM_X86_BARRIER_H
   2 #define _ASM_X86_BARRIER_H
   3
   4 #include <asm/alternative.h>
   5 #include <asm/nops.h>
   6
   7 /*
   8  * Force strict CPU ordering.
   9  * And yes, this is required on UP too when we're talking
  10  * to devices.
  11  */
  12
  13 #ifdef CONFIG_X86_32
  14 /*
  15  * Some non-Intel clones support out of order store. wmb() ceases to be a
  16  * nop for these.
  17  */
  18 #define mb() alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2)
  19 #define rmb() alternative("lock; addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2)
  20 #define wmb() alternative("lock; addl $0,0(%%esp)", "sfence", X86_FEATURE_XMM)
  21 #else
  22 #define mb()    asm volatile("mfence":::"memory")
  23 #define rmb()   asm volatile("lfence":::"memory")
  24 #define wmb()   asm volatile("sfence" ::: "memory")
  25 #endif
  26
  27 #ifdef CONFIG_X86_PPRO_FENCE
  28 #define dma_rmb()       rmb()
  29 #else
  30 #define dma_rmb()       barrier()
  31 #endif
  32 #define dma_wmb()       barrier()
  33
  34 #ifdef CONFIG_SMP
  35 #define smp_mb()        mb()
  36 #define smp_rmb()       dma_rmb()
  37 #define smp_wmb()       barrier()
  38 #define set_mb(var, value) do { (void)xchg(&var, value); } while (0)
  39 #else /* !SMP */
  40 #define smp_mb()        barrier()
  41 #define smp_rmb()       barrier()
  42 #define smp_wmb()       barrier()
  43 #define set_mb(var, value) do { var = value; barrier(); } while (0)
  44 #endif /* SMP */
  45
  46 #define read_barrier_depends()          do { } while (0)
  47 #define smp_read_barrier_depends()      do { } while (0)
  48
  49 #if defined(CONFIG_X86_PPRO_FENCE)
  50
  51 /*
  52  * For this option x86 doesn't have a strong TSO memory
  53  * model and we should fall back to full barriers.
  54  */
  55
  56 #define smp_store_release(p, v)                                         \
  57 do {                                                                    \
  58         compiletime_assert_atomic_type(*p);                             \
  59         smp_mb();                                                       \
  60         ACCESS_ONCE(*p) = (v);                                          \
  61 } while (0)
  62
  63 #define smp_load_acquire(p)                                             \
  64 ({                                                                      \
  65         typeof(*p) ___p1 = ACCESS_ONCE(*p);                             \
  66         compiletime_assert_atomic_type(*p);                             \
  67         smp_mb();                                                       \
  68         ___p1;                                                          \
  69 })
  70
  71 #else /* regular x86 TSO memory ordering */
  72
  73 #define smp_store_release(p, v)                                         \
  74 do {                                                                    \
  75         compiletime_assert_atomic_type(*p);                             \
  76         barrier();                                                      \
  77         ACCESS_ONCE(*p) = (v);                                          \
  78 } while (0)
  79
  80 #define smp_load_acquire(p)                                             \
  81 ({                                                                      \
  82         typeof(*p) ___p1 = ACCESS_ONCE(*p);                             \
  83         compiletime_assert_atomic_type(*p);                             \
  84         barrier();                                                      \
  85         ___p1;                                                          \
  86 })
  87
  88 #endif
  89
  90 /* Atomic operations are already serializing on x86 */
  91 #define smp_mb__before_atomic() barrier()
  92 #define smp_mb__after_atomic()  barrier()
  93
  94 /*
  95  * Stop RDTSC speculation. This is needed when you need to use RDTSC
  96  * (or get_cycles or vread that possibly accesses the TSC) in a defined
  97  * code region.
  98  *
  99  * (Could use an alternative three way for this if there was one.)
 100  */
 101 static __always_inline void rdtsc_barrier(void)
 102 {
 103         alternative(ASM_NOP3, "mfence", X86_FEATURE_MFENCE_RDTSC);
 104         alternative(ASM_NOP3, "lfence", X86_FEATURE_LFENCE_RDTSC);
 105 }
 106
 107 #endif /* _ASM_X86_BARRIER_H */