x86, asm: Merge cmpxchg_486_u64() and cmpxchg8b_emu()

We have two functions for doing exactly the same thing -- emulating
cmpxchg8b on 486 and older hardware -- with different calling
conventions, and yet doing the same thing.  Drop the C version and use
the assembly version, via alternatives, for both the local and
non-local versions of cmpxchg8b.

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
LKML-Reference: <AANLkTikAmaDPji-TVDarmG1yD=fwbffcsmEU=YEuP+8r@mail.gmail.com>

2 files changed, 14 insertions, 34 deletions

diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index f5bd1fd388ff..284a6e8f7ce1 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -246,8 +246,6 @@ static inline unsigned long cmpxchg_386(volatile void *ptr, unsigned long old,
  * to simulate the cmpxchg8b on the 80386 and 80486 CPU.
  */
 
-extern unsigned long long cmpxchg_486_u64(volatile void *, u64, u64);
-
 #define cmpxchg64(ptr, o, n)                                    \
 ({                                                              \
         __typeof__(*(ptr)) __ret;                               \
@@ -265,20 +263,20 @@ extern unsigned long long cmpxchg_486_u64(volatile void *, u64, u64);
         __ret; })
 
 
-
-#define cmpxchg64_local(ptr, o, n)                                      \
-({                                                                      \
-        __typeof__(*(ptr)) __ret;                                       \
-        if (likely(boot_cpu_data.x86 > 4))                              \
-                __ret = (__typeof__(*(ptr)))__cmpxchg64_local((ptr),    \
-                                (unsigned long long)(o),                \
-                                (unsigned long long)(n));               \
-        else                                                            \
-                __ret = (__typeof__(*(ptr)))cmpxchg_486_u64((ptr),      \
-                                (unsigned long long)(o),                \
-                                (unsigned long long)(n));               \
-        __ret;                                                          \
-})
+#define cmpxchg64_local(ptr, o, n)                              \
+({                                                              \
+        __typeof__(*(ptr)) __ret;                               \
+        __typeof__(*(ptr)) __old = (o);                         \
+        __typeof__(*(ptr)) __new = (n);                         \
+        alternative_io("call cmpxchg8b_emu",                    \
+                       "cmpxchg8b (%%esi)" ,                    \
+                       X86_FEATURE_CX8,                         \
+                       "=A" (__ret),                            \
+                       "S" ((ptr)), "0" (__old),                \
+                       "b" ((unsigned int)__new),               \
+                       "c" ((unsigned int)(__new>>32))          \
+                       : "memory");                             \
+        __ret; })
 
 #endif
 
diff --git a/arch/x86/lib/cmpxchg.c b/arch/x86/lib/cmpxchg.c
index 2056ccf572cc..5d619f6df3ee 100644
--- a/arch/x86/lib/cmpxchg.c
+++ b/arch/x86/lib/cmpxchg.c
@@ -52,21 +52,3 @@ unsigned long cmpxchg_386_u32(volatile void *ptr, u32 old, u32 new)
 }
 EXPORT_SYMBOL(cmpxchg_386_u32);
 #endif
-
-#ifndef CONFIG_X86_CMPXCHG64
-unsigned long long cmpxchg_486_u64(volatile void *ptr, u64 old, u64 new)
-{
-        u64 prev;
-        unsigned long flags;
-
-        /* Poor man's cmpxchg8b for 386 and 486. Unsuitable for SMP */
-        local_irq_save(flags);
-        prev = *(u64 *)ptr;
-        if (prev == old)
-                *(u64 *)ptr = new;
-        local_irq_restore(flags);
-        return prev;
-}
-EXPORT_SYMBOL(cmpxchg_486_u64);
-#endif
-