diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index cc8c501b9f39..867ff94579be 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -342,5 +342,22 @@ 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
+
 // arch_initcall(intel_cpu_init);
 
diff --git a/include/asm-x86/cmpxchg_32.h b/include/asm-x86/cmpxchg_32.h
index f86ede28f6dc..cea1dae288a7 100644
--- a/include/asm-x86/cmpxchg_32.h
+++ b/include/asm-x86/cmpxchg_32.h
@@ -105,15 +105,24 @@ static inline unsigned long __xchg(unsigned long x, volatile void * ptr, int siz
 
 #ifdef CONFIG_X86_CMPXCHG
 #define __HAVE_ARCH_CMPXCHG 1
-#define cmpxchg(ptr,o,n)\
-	((__typeof__(*(ptr)))__cmpxchg((ptr),(unsigned long)(o),\
-					(unsigned long)(n),sizeof(*(ptr))))
-#define sync_cmpxchg(ptr,o,n)\
-	((__typeof__(*(ptr)))__sync_cmpxchg((ptr),(unsigned long)(o),\
-					(unsigned long)(n),sizeof(*(ptr))))
-#define cmpxchg_local(ptr,o,n)\
-	((__typeof__(*(ptr)))__cmpxchg_local((ptr),(unsigned long)(o),\
-					(unsigned long)(n),sizeof(*(ptr))))
+#define cmpxchg(ptr, o, n)						     \
+	((__typeof__(*(ptr)))__cmpxchg((ptr), (unsigned long)(o),	     \
+					(unsigned long)(n), sizeof(*(ptr))))
+#define sync_cmpxchg(ptr, o, n)						     \
+	((__typeof__(*(ptr)))__sync_cmpxchg((ptr), (unsigned long)(o),	     \
+					(unsigned long)(n), sizeof(*(ptr))))
+#define cmpxchg_local(ptr, o, n)					     \
+	((__typeof__(*(ptr)))__cmpxchg_local((ptr), (unsigned long)(o),	     \
+					(unsigned long)(n), sizeof(*(ptr))))
+#endif
+
+#ifdef CONFIG_X86_CMPXCHG64
+#define cmpxchg64(ptr, o, n)						      \
+	((__typeof__(*(ptr)))__cmpxchg64((ptr), (unsigned long long)(o),      \
+					(unsigned long long)(n)))
+#define cmpxchg64_local(ptr, o, n)					      \
+	((__typeof__(*(ptr)))__cmpxchg64_local((ptr), (unsigned long long)(o),\
+					(unsigned long long)(n)))
 #endif
 
 static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
@@ -203,57 +212,8 @@ static inline unsigned long __cmpxchg_local(volatile void *ptr,
 	return old;
 }
 
-#ifndef CONFIG_X86_CMPXCHG
-/*
- * Building a kernel capable running on 80386. It may be necessary to
- * simulate the cmpxchg on the 80386 CPU. For that purpose we define
- * a function for each of the sizes we support.
- */
-
-extern unsigned long cmpxchg_386_u8(volatile void *, u8, u8);
-extern unsigned long cmpxchg_386_u16(volatile void *, u16, u16);
-extern unsigned long cmpxchg_386_u32(volatile void *, u32, u32);
-
-static inline unsigned long cmpxchg_386(volatile void *ptr, unsigned long old,
-				      unsigned long new, int size)
-{
-	switch (size) {
-	case 1:
-		return cmpxchg_386_u8(ptr, old, new);
-	case 2:
-		return cmpxchg_386_u16(ptr, old, new);
-	case 4:
-		return cmpxchg_386_u32(ptr, old, new);
-	}
-	return old;
-}
-
-#define cmpxchg(ptr,o,n)						\
-({									\
-	__typeof__(*(ptr)) __ret;					\
-	if (likely(boot_cpu_data.x86 > 3))				\
-		__ret = __cmpxchg((ptr), (unsigned long)(o),		\
-					(unsigned long)(n), sizeof(*(ptr))); \
-	else								\
-		__ret = cmpxchg_386((ptr), (unsigned long)(o),		\
-					(unsigned long)(n), sizeof(*(ptr))); \
-	__ret;								\
-})
-#define cmpxchg_local(ptr,o,n)						\
-({									\
-	__typeof__(*(ptr)) __ret;					\
-	if (likely(boot_cpu_data.x86 > 3))				\
-		__ret = __cmpxchg_local((ptr), (unsigned long)(o),	\
-					(unsigned long)(n), sizeof(*(ptr))); \
-	else								\
-		__ret = cmpxchg_386((ptr), (unsigned long)(o),		\
-					(unsigned long)(n), sizeof(*(ptr))); \
-	__ret;								\
-})
-#endif
-
-static inline unsigned long long __cmpxchg64(volatile void *ptr, unsigned long long old,
-				      unsigned long long new)
+static inline unsigned long long __cmpxchg64(volatile void *ptr,
+			unsigned long long old, unsigned long long new)
 {
 	unsigned long long prev;
 	__asm__ __volatile__(LOCK_PREFIX "cmpxchg8b %3"
@@ -280,10 +240,86 @@ static inline unsigned long long __cmpxchg64_local(volatile void *ptr,
 	return prev;
 }
 
-#define cmpxchg64(ptr,o,n)\
-	((__typeof__(*(ptr)))__cmpxchg64((ptr),(unsigned long long)(o),\
-					(unsigned long long)(n)))
-#define cmpxchg64_local(ptr,o,n)\
-	((__typeof__(*(ptr)))__cmpxchg64_local((ptr),(unsigned long long)(o),\
-					(unsigned long long)(n)))
+#ifndef CONFIG_X86_CMPXCHG
+/*
+ * Building a kernel capable running on 80386. It may be necessary to
+ * simulate the cmpxchg on the 80386 CPU. For that purpose we define
+ * a function for each of the sizes we support.
+ */
+
+extern unsigned long cmpxchg_386_u8(volatile void *, u8, u8);
+extern unsigned long cmpxchg_386_u16(volatile void *, u16, u16);
+extern unsigned long cmpxchg_386_u32(volatile void *, u32, u32);
+
+static inline unsigned long cmpxchg_386(volatile void *ptr, unsigned long old,
+				      unsigned long new, int size)
+{
+	switch (size) {
+	case 1:
+		return cmpxchg_386_u8(ptr, old, new);
+	case 2:
+		return cmpxchg_386_u16(ptr, old, new);
+	case 4:
+		return cmpxchg_386_u32(ptr, old, new);
+	}
+	return old;
+}
+
+#define cmpxchg(ptr, o, n)						\
+({									\
+	__typeof__(*(ptr)) __ret;					\
+	if (likely(boot_cpu_data.x86 > 3))				\
+		__ret = __cmpxchg((ptr), (unsigned long)(o),		\
+					(unsigned long)(n), sizeof(*(ptr))); \
+	else								\
+		__ret = cmpxchg_386((ptr), (unsigned long)(o),		\
+					(unsigned long)(n), sizeof(*(ptr))); \
+	__ret;								\
+})
+#define cmpxchg_local(ptr, o, n)					\
+({									\
+	__typeof__(*(ptr)) __ret;					\
+	if (likely(boot_cpu_data.x86 > 3))				\
+		__ret = __cmpxchg_local((ptr), (unsigned long)(o),	\
+					(unsigned long)(n), sizeof(*(ptr))); \
+	else								\
+		__ret = cmpxchg_386((ptr), (unsigned long)(o),		\
+					(unsigned long)(n), sizeof(*(ptr))); \
+	__ret;								\
+})
+#endif
+
+#ifndef CONFIG_X86_CMPXCHG64
+/*
+ * Building a kernel capable running on 80386 and 80486. It may be necessary
+ * 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;					\
+	if (likely(boot_cpu_data.x86 > 4))				\
+		__ret = __cmpxchg64((ptr), (unsigned long long)(o),	\
+				(unsigned long long)(n));		\
+	else								\
+		__ret = cmpxchg_486_u64((ptr), (unsigned long long)(o),	\
+				(unsigned long long)(n));		\
+	__ret;								\
+})
+#define cmpxchg64_local(ptr, o, n)					\
+({									\
+	__typeof__(*(ptr)) __ret;					\
+	if (likely(boot_cpu_data.x86 > 4))				\
+		__ret = __cmpxchg64_local((ptr), (unsigned long long)(o), \
+				(unsigned long long)(n));		\
+	else								\
+		__ret = cmpxchg_486_u64((ptr), (unsigned long long)(o),	\
+				(unsigned long long)(n));		\
+	__ret;								\
+})
+
+#endif
+
 #endif