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

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;								\
-})
+	__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
 

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
-