[slubll1 08/19] x86: Add support for cmpxchg_double

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A simple implementation that only supports the word size and does not
have a fallback mode (would require a spinlock).

And 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 the support of that feature
during kernel builds.

Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>

---
 arch/x86/Kconfig.cpu              |    3 ++
 arch/x86/include/asm/cmpxchg_32.h |   46 ++++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/cmpxchg_64.h |   43 +++++++++++++++++++++++++++++++++++
 3 files changed, 92 insertions(+)

Index: linux-2.6/arch/x86/include/asm/cmpxchg_64.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/cmpxchg_64.h	2011-03-30 11:21:40.000000000 -0500
+++ linux-2.6/arch/x86/include/asm/cmpxchg_64.h	2011-03-30 12:31:35.000000000 -0500
@@ -151,4 +151,47 @@ extern void __cmpxchg_wrong_size(void);
 	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_HERE "lock; cmpxchg16b (%%rsi);setz %1" \
+		       : "=d"(__junk), "=a"(__ret)		\
+		       : "S"(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 (%%rsi)\n\t\tsetz %1\n\t"	\
+		       : "=d"(__junk)_, "=a"(__ret)		\
+		       : "S"((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));		\
+})
+
 #endif /* _ASM_X86_CMPXCHG_64_H */
Index: linux-2.6/arch/x86/include/asm/cmpxchg_32.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/cmpxchg_32.h	2011-03-30 11:21:40.000000000 -0500
+++ linux-2.6/arch/x86/include/asm/cmpxchg_32.h	2011-03-30 12:40:27.000000000 -0500
@@ -280,4 +280,50 @@ static inline unsigned long cmpxchg_386(
 
 #endif
 
+#define cmpxchg8b(ptr, o1, o2, n1, n2)				\
+({								\
+	char __ret;						\
+	__typeof__(o2) __dummy;					\
+	__typeof__(*(ptr)) __old1 = (o1);			\
+	__typeof__(o2) __old2 = (o2);				\
+	__typeof__(*(ptr)) __new1 = (n1);			\
+	__typeof__(o2) __new2 = (n2);				\
+	asm volatile(LOCK_PREFIX_HERE "lock; cmpxchg8b (%%esi); setz %1"\
+		       : "d="(__dummy), "=a" (__ret) 		\
+		       : "S" ((ptr)), "a" (__old1), "d"(__old2),	\
+		         "b" (__new1), "c" (__new2)		\
+		       : "memory");				\
+	__ret; })
+
+
+#define cmpxchg8b_local(ptr, o1, o2, n1, n2)			\
+({								\
+	char __ret;						\
+	__typeof__(o2) __dummy;					\
+	__typeof__(*(ptr)) __old1 = (o1);			\
+	__typeof__(o2) __old2 = (o2);				\
+	__typeof__(*(ptr)) __new1 = (n1);			\
+	__typeof__(o2) __new2 = (n2);				\
+	asm volatile("cmpxchg8b (%%esi); tsetz %1"		\
+		       : "d="(__dummy), "=a"(__ret)		\
+		       : "S" ((ptr)), "a" (__old), "d"(__old2),	\
+		         "b" (__new1), "c" (__new2),		\
+		       : "memory");				\
+	__ret; })
+
+
+#define cmpxchg_double(ptr, o1, o2, n1, n2)				\
+({									\
+	BUILD_BUG_ON(sizeof(*(ptr)) != 4);				\
+	VM_BUG_ON((unsigned long)(ptr) % 8);				\
+	cmpxchg8b((ptr), (o1), (o2), (n1), (n2));			\
+})
+
+#define cmpxchg_double_local(ptr, o1, o2, n1, n2)			\
+({									\
+       BUILD_BUG_ON(sizeof(*(ptr)) != 4);				\
+       VM_BUG_ON((unsigned long)(ptr) % 8);				\
+       cmpxchg16b_local((ptr), (o1), (o2), (n1), (n2));			\
+})
+
 #endif /* _ASM_X86_CMPXCHG_32_H */
Index: linux-2.6/arch/x86/Kconfig.cpu
===================================================================
--- linux-2.6.orig/arch/x86/Kconfig.cpu	2011-03-30 11:21:40.000000000 -0500
+++ linux-2.6/arch/x86/Kconfig.cpu	2011-03-30 11:21:44.000000000 -0500
@@ -308,6 +308,9 @@ config X86_CMPXCHG
 config CMPXCHG_LOCAL
 	def_bool X86_64 || (X86_32 && !M386)
 
+config CMPXCHG_DOUBLE
+	def_bool X86_64 || (X86_32 && !M386)
+
 config X86_L1_CACHE_SHIFT
 	int
 	default "7" if MPENTIUM4 || MPSC

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