4 files changed, 83 insertions, 14 deletions

diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index 82ceb788a98..ee1931be659 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -312,19 +312,23 @@ static inline unsigned long cmpxchg_386(volatile void *ptr, unsigned long old,
 
 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 = (__typeof__(*(ptr)))__cmpxchg64((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(ptr, o, n)                                    \
+({                                                              \
+        __typeof__(*(ptr)) __ret;                               \
+        __typeof__(*(ptr)) __old = (o);                         \
+        __typeof__(*(ptr)) __new = (n);                         \
+        alternative_io("call cmpxchg8b_emu",                    \
+                        "lock; cmpxchg8b (%%esi)" ,             \
+                       X86_FEATURE_CX8,                         \
+                       "=A" (__ret),                            \
+                       "S" ((ptr)), "0" (__old),                \
+                       "b" ((unsigned int)__new),               \
+                       "c" ((unsigned int)(__new>>32))          \
+                       : "memory");                             \
+        __ret; })
+
+
+
 #define cmpxchg64_local(ptr, o, n)                                      \
 ({                                                                      \
         __typeof__(*(ptr)) __ret;                                       \
diff --git a/arch/x86/kernel/i386_ksyms_32.c b/arch/x86/kernel/i386_ksyms_32.c
index 43cec6bdda6..1736c5a725a 100644
--- a/arch/x86/kernel/i386_ksyms_32.c
+++ b/arch/x86/kernel/i386_ksyms_32.c
@@ -10,6 +10,14 @@
 EXPORT_SYMBOL(mcount);
 #endif
 
+/*
+ * Note, this is a prototype to get at the symbol for
+ * the export, but dont use it from C code, it is used
+ * by assembly code and is not using C calling convention!
+ */
+extern void cmpxchg8b_emu(void);
+EXPORT_SYMBOL(cmpxchg8b_emu);
+
 /* Networking helper routines. */
 EXPORT_SYMBOL(csum_partial_copy_generic);
 
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 9e609206fac..3e549b8ec8c 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -15,7 +15,7 @@ ifeq ($(CONFIG_X86_32),y)
         obj-y += atomic64_32.o
         lib-y += checksum_32.o
         lib-y += strstr_32.o
-        lib-y += semaphore_32.o string_32.o
+        lib-y += semaphore_32.o string_32.o cmpxchg8b_emu.o
 
         lib-$(CONFIG_X86_USE_3DNOW) += mmx_32.o
 else
diff --git a/arch/x86/lib/cmpxchg8b_emu.S b/arch/x86/lib/cmpxchg8b_emu.S
new file mode 100644
index 00000000000..828cb710dec
--- /dev/null
+++ b/arch/x86/lib/cmpxchg8b_emu.S
@@ -0,0 +1,57 @@
+/*
+ *      This program is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU General Public License
+ *      as published by the Free Software Foundation; version 2
+ *      of the License.
+ *
+ */
+
+#include <linux/linkage.h>
+#include <asm/alternative-asm.h>
+#include <asm/frame.h>
+#include <asm/dwarf2.h>
+
+
+.text
+
+/*
+ * Inputs:
+ * %esi : memory location to compare
+ * %eax : low 32 bits of old value
+ * %edx : high 32 bits of old value
+ * %ebx : low 32 bits of new value
+ * %ecx : high 32 bits of new value
+ */
+ENTRY(cmpxchg8b_emu)
+CFI_STARTPROC
+
+#
+# Emulate 'cmpxchg8b (%esi)' on UP except we don't
+# set the whole ZF thing (caller will just compare
+# eax:edx with the expected value)
+#
+cmpxchg8b_emu:
+        pushfl
+        cli
+
+        cmpl  (%esi), %eax
+        jne not_same
+        cmpl 4(%esi), %edx
+        jne half_same
+
+        movl %ebx,  (%esi)
+        movl %ecx, 4(%esi)
+
+        popfl
+        ret
+
+ not_same:
+        movl  (%esi), %eax
+ half_same:
+        movl 4(%esi), %edx
+
+        popfl
+        ret
+
+CFI_ENDPROC
+ENDPROC(cmpxchg8b_emu)