percpu: Omit segment prefix in the UP case for cmpxchg_double

Omit the segment prefix in the UP case. GS is not used then
and we will generate segfaults if cmpxchg16b is used otherwise.

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 16 insertions, 8 deletions

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index a09e1f052d84..d475b4398d8b 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -45,7 +45,7 @@
 #include <linux/stringify.h>
 
 #ifdef CONFIG_SMP
-#define __percpu_arg(x)         "%%"__stringify(__percpu_seg)":%P" #x
+#define __percpu_prefix         "%%"__stringify(__percpu_seg)":"
 #define __my_cpu_offset         percpu_read(this_cpu_off)
 
 /*
@@ -62,9 +62,11 @@
         (typeof(*(ptr)) __kernel __force *)tcp_ptr__;   \
 })
 #else
-#define __percpu_arg(x)         "%P" #x
+#define __percpu_prefix         ""
 #endif
 
+#define __percpu_arg(x)         __percpu_prefix "%P" #x
+
 /*
  * Initialized pointers to per-cpu variables needed for the boot
  * processor need to use these macros to get the proper address
@@ -516,11 +518,11 @@ do {									\
         typeof(o2) __n2 = n2;                                           \
         typeof(o2) __dummy;                                             \
         alternative_io("call this_cpu_cmpxchg16b_emu\n\t" P6_NOP4,      \
-                       "cmpxchg16b %%gs:(%%rsi)\n\tsetz %0\n\t",        \
+                       "cmpxchg16b " __percpu_prefix "(%%rsi)\n\tsetz %0\n\t",  \
                        X86_FEATURE_CX16,                                \
                        ASM_OUTPUT2("=a"(__ret), "=d"(__dummy)),         \
                        "S" (&pcp1), "b"(__n1), "c"(__n2),               \
-                       "a"(__o1), "d"(__o2));                           \
+                       "a"(__o1), "d"(__o2) : "memory");                \
         __ret;                                                          \
 })
 
diff --git a/arch/x86/lib/cmpxchg16b_emu.S b/arch/x86/lib/cmpxchg16b_emu.S
index 3e8b08a6de2b..1e572c507d06 100644
--- a/arch/x86/lib/cmpxchg16b_emu.S
+++ b/arch/x86/lib/cmpxchg16b_emu.S
@@ -10,6 +10,12 @@
 #include <asm/frame.h>
 #include <asm/dwarf2.h>
 
+#ifdef CONFIG_SMP
+#define SEG_PREFIX %gs:
+#else
+#define SEG_PREFIX
+#endif
+
 .text
 
 /*
@@ -37,13 +43,13 @@ this_cpu_cmpxchg16b_emu:
         pushf
         cli
 
-        cmpq %gs:(%rsi), %rax
+        cmpq SEG_PREFIX(%rsi), %rax
         jne not_same
-        cmpq %gs:8(%rsi), %rdx
+        cmpq SEG_PREFIX 8(%rsi), %rdx
         jne not_same
 
-        movq %rbx, %gs:(%rsi)
-        movq %rcx, %gs:8(%rsi)
+        movq %rbx, SEG_PREFIX(%rsi)
+        movq %rcx, SEG_PREFIX 8(%rsi)
 
         popf
         mov $1, %al