arch/x86/include/asm/cmpxchg_32.h

   1 #ifndef _ASM_X86_CMPXCHG_32_H
   2 #define _ASM_X86_CMPXCHG_32_H
   3
   4 /*
   5  * Note: if you use set64_bit(), __cmpxchg64(), or their variants, you
   6  *       you need to test for the feature in boot_cpu_data.
   7  */
   8
   9 /*
  10  * CMPXCHG8B only writes to the target if we had the previous
  11  * value in registers, otherwise it acts as a read and gives us the
  12  * "new previous" value.  That is why there is a loop.  Preloading
  13  * EDX:EAX is a performance optimization: in the common case it means
  14  * we need only one locked operation.
  15  *
  16  * A SIMD/3DNOW!/MMX/FPU 64-bit store here would require at the very
  17  * least an FPU save and/or %cr0.ts manipulation.
  18  *
  19  * cmpxchg8b must be used with the lock prefix here to allow the
  20  * instruction to be executed atomically.  We need to have the reader
  21  * side to see the coherent 64bit value.
  22  */
  23 static inline void set_64bit(volatile u64 *ptr, u64 value)
  24 {
  25         u32 low  = value;
  26         u32 high = value >> 32;
  27         u64 prev = *ptr;
  28
  29         asm volatile("\n1:\t"
  30                      LOCK_PREFIX "cmpxchg8b %0\n\t"
  31                      "jnz 1b"
  32                      : "=m" (*ptr), "+A" (prev)
  33                      : "b" (low), "c" (high)
  34                      : "memory");
  35 }
  36
  37 #ifdef CONFIG_X86_CMPXCHG64
  38 #define cmpxchg64(ptr, o, n)                                            \
  39         ((__typeof__(*(ptr)))__cmpxchg64((ptr), (unsigned long long)(o), \
  40                                          (unsigned long long)(n)))
  41 #define cmpxchg64_local(ptr, o, n)                                      \
  42         ((__typeof__(*(ptr)))__cmpxchg64_local((ptr), (unsigned long long)(o), \
  43                                                (unsigned long long)(n)))
  44 #endif
  45
  46 static inline u64 __cmpxchg64(volatile u64 *ptr, u64 old, u64 new)
  47 {
  48         u64 prev;
  49         asm volatile(LOCK_PREFIX "cmpxchg8b %1"
  50                      : "=A" (prev),
  51                        "+m" (*ptr)
  52                      : "b" ((u32)new),
  53                        "c" ((u32)(new >> 32)),
  54                        "0" (old)
  55                      : "memory");
  56         return prev;
  57 }
  58
  59 static inline u64 __cmpxchg64_local(volatile u64 *ptr, u64 old, u64 new)
  60 {
  61         u64 prev;
  62         asm volatile("cmpxchg8b %1"
  63                      : "=A" (prev),
  64                        "+m" (*ptr)
  65                      : "b" ((u32)new),
  66                        "c" ((u32)(new >> 32)),
  67                        "0" (old)
  68                      : "memory");
  69         return prev;
  70 }
  71
  72 #ifndef CONFIG_X86_CMPXCHG64
  73 /*
  74  * Building a kernel capable running on 80386 and 80486. It may be necessary
  75  * to simulate the cmpxchg8b on the 80386 and 80486 CPU.
  76  */
  77
  78 #define cmpxchg64(ptr, o, n)                                    \
  79 ({                                                              \
  80         __typeof__(*(ptr)) __ret;                               \
  81         __typeof__(*(ptr)) __old = (o);                         \
  82         __typeof__(*(ptr)) __new = (n);                         \
  83         alternative_io(LOCK_PREFIX_HERE                         \
  84                         "call cmpxchg8b_emu",                   \
  85                         "lock; cmpxchg8b (%%esi)" ,             \
  86                        X86_FEATURE_CX8,                         \
  87                        "=A" (__ret),                            \
  88                        "S" ((ptr)), "0" (__old),                \
  89                        "b" ((unsigned int)__new),               \
  90                        "c" ((unsigned int)(__new>>32))          \
  91                        : "memory");                             \
  92         __ret; })
  93
  94
  95 #define cmpxchg64_local(ptr, o, n)                              \
  96 ({                                                              \
  97         __typeof__(*(ptr)) __ret;                               \
  98         __typeof__(*(ptr)) __old = (o);                         \
  99         __typeof__(*(ptr)) __new = (n);                         \
 100         alternative_io("call cmpxchg8b_emu",                    \
 101                        "cmpxchg8b (%%esi)" ,                    \
 102                        X86_FEATURE_CX8,                         \
 103                        "=A" (__ret),                            \
 104                        "S" ((ptr)), "0" (__old),                \
 105                        "b" ((unsigned int)__new),               \
 106                        "c" ((unsigned int)(__new>>32))          \
 107                        : "memory");                             \
 108         __ret; })
 109
 110 #endif
 111
 112 #define system_has_cmpxchg_double() boot_cpu_has(X86_FEATURE_CX8)
 113
 114 #endif /* _ASM_X86_CMPXCHG_32_H */