x86: Add support for cmpxchg_double
A simple implementation that only supports the word size and does not
have a fallback mode (would require a spinlock).
Add 32 and 64 bit support for cmpxchg_double. cmpxchg double uses
the cmpxchg8b or cmpxchg16b instruction on x86 processors to compare
and swap 2 machine words. This allows lockless algorithms to move more
context information through critical sections.
Set a flag CONFIG_CMPXCHG_DOUBLE to signal that support for double word
cmpxchg detection has been build into the kernel. Note that each subsystem
using cmpxchg_double has to implement a fall back mechanism as long as
we offer support for processors that do not implement cmpxchg_double.
Reviewed-by: H. Peter Anvin <hpa@zytor.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Christoph Lameter <cl@linux.com>
Link: http://lkml.kernel.org/r/20110601172614.173427964@linux.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
index 423ae58..7cf5c0a 100644
--- a/arch/x86/include/asm/cmpxchg_64.h
+++ b/arch/x86/include/asm/cmpxchg_64.h
@@ -151,4 +151,49 @@
cmpxchg_local((ptr), (o), (n)); \
})
+#define cmpxchg16b(ptr, o1, o2, n1, n2) \
+({ \
+ char __ret; \
+ __typeof__(o2) __junk; \
+ __typeof__(*(ptr)) __old1 = (o1); \
+ __typeof__(o2) __old2 = (o2); \
+ __typeof__(*(ptr)) __new1 = (n1); \
+ __typeof__(o2) __new2 = (n2); \
+ asm volatile(LOCK_PREFIX "cmpxchg16b %2;setz %1" \
+ : "=d"(__junk), "=a"(__ret), "+m" (*ptr) \
+ : "b"(__new1), "c"(__new2), \
+ "a"(__old1), "d"(__old2)); \
+ __ret; })
+
+
+#define cmpxchg16b_local(ptr, o1, o2, n1, n2) \
+({ \
+ char __ret; \
+ __typeof__(o2) __junk; \
+ __typeof__(*(ptr)) __old1 = (o1); \
+ __typeof__(o2) __old2 = (o2); \
+ __typeof__(*(ptr)) __new1 = (n1); \
+ __typeof__(o2) __new2 = (n2); \
+ asm volatile("cmpxchg16b %2;setz %1" \
+ : "=d"(__junk), "=a"(__ret), "+m" (*ptr) \
+ : "b"(__new1), "c"(__new2), \
+ "a"(__old1), "d"(__old2)); \
+ __ret; })
+
+#define cmpxchg_double(ptr, o1, o2, n1, n2) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ VM_BUG_ON((unsigned long)(ptr) % 16); \
+ cmpxchg16b((ptr), (o1), (o2), (n1), (n2)); \
+})
+
+#define cmpxchg_double_local(ptr, o1, o2, n1, n2) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ VM_BUG_ON((unsigned long)(ptr) % 16); \
+ cmpxchg16b_local((ptr), (o1), (o2), (n1), (n2)); \
+})
+
+#define system_has_cmpxchg_double() cpu_has_cx16
+
#endif /* _ASM_X86_CMPXCHG_64_H */