From: Heiko Carstens <hca@linux.ibm.com>
Date: Wed, 6 Nov 2024 10:03:07 +0000 (+0100)
Subject: s390/cmpxchg: Provide arch_try_cmpxchg()
X-Git-Tag: v6.13-rc1~206^2~37
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0b6de9aec285d24d49a918d52915ed231b2d9e87;p=thirdparty%2Fkernel%2Flinux.git

s390/cmpxchg: Provide arch_try_cmpxchg()

Since gcc 14 flag output operands are supported also for s390.

Provide an arch_try_cmpxchg() implementation so that all existing
try_cmpxchg() variants provide slightly better code, if compiled
with gcc 14 or newer.

Reviewed-by: Juergen Christ <jchrist@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---

diff --git a/arch/s390/include/asm/asm.h b/arch/s390/include/asm/asm.h
new file mode 100644
index 0000000000000..bea9dcf9e70e7
--- /dev/null
+++ b/arch/s390/include/asm/asm.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_ASM_H
+#define _ASM_S390_ASM_H
+
+/* GCC versions before 14.2.0 may die with an ICE in some configurations. */
+#if defined(__GCC_ASM_FLAG_OUTPUTS__) && !(IS_ENABLED(CONFIG_CC_IS_GCC) && (GCC_VERSION < 140200))
+
+#define __HAVE_ASM_FLAG_OUTPUTS__
+
+#endif
+
+#endif /* _ASM_S390_ASM_H */
diff --git a/arch/s390/include/asm/cmpxchg.h b/arch/s390/include/asm/cmpxchg.h
index 5875296733990..05f123d39bc3c 100644
--- a/arch/s390/include/asm/cmpxchg.h
+++ b/arch/s390/include/asm/cmpxchg.h
@@ -11,6 +11,7 @@
 #include <linux/mmdebug.h>
 #include <linux/types.h>
 #include <linux/bug.h>
+#include <asm/asm.h>
 
 void __xchg_called_with_bad_pointer(void);
 
@@ -174,6 +175,57 @@ static __always_inline u64 __arch_cmpxchg(u64 ptr, u64 old, u64 new, int size)
 #define arch_cmpxchg_local	arch_cmpxchg
 #define arch_cmpxchg64_local	arch_cmpxchg
 
+#ifdef __HAVE_ASM_FLAG_OUTPUTS__
+
+#define arch_try_cmpxchg(ptr, oldp, new)				\
+({									\
+	__typeof__(ptr) __oldp = (__typeof__(ptr))(oldp);		\
+	__typeof__(*(ptr)) __old = *__oldp;				\
+	__typeof__(*(ptr)) __new = (new);				\
+	__typeof__(*(ptr)) __prev;					\
+	int __cc;							\
+									\
+	switch (sizeof(*(ptr))) {					\
+	case 1:								\
+	case 2: {							\
+		__prev = arch_cmpxchg((ptr), (__old), (__new));		\
+		__cc = (__prev != __old);				\
+		if (unlikely(__cc))					\
+			*__oldp = __prev;				\
+		break;							\
+	}								\
+	case 4:	{							\
+		asm volatile(						\
+			"	cs	%[__old],%[__new],%[__ptr]\n"	\
+			: [__old] "+d" (*__oldp),			\
+			  [__ptr] "+Q" (*(ptr)),			\
+			  "=@cc" (__cc)					\
+			: [__new] "d" (__new)				\
+			: "memory");					\
+		break;							\
+	}								\
+	case 8:	{							\
+		 asm volatile(						\
+			 "	csg	%[__old],%[__new],%[__ptr]\n"	\
+			 : [__old] "+d" (*__oldp),			\
+			   [__ptr] "+QS" (*(ptr)),			\
+			   "=@cc" (__cc)				\
+			 : [__new] "d" (__new)				\
+			 : "memory");					\
+		 break;							\
+	}								\
+	default:							\
+		__cmpxchg_called_with_bad_pointer();			\
+	}								\
+	likely(__cc == 0);						\
+})
+
+#define arch_try_cmpxchg64		arch_try_cmpxchg
+#define arch_try_cmpxchg_local		arch_try_cmpxchg
+#define arch_try_cmpxchg64_local	arch_try_cmpxchg
+
+#endif /* __HAVE_ASM_FLAG_OUTPUTS__ */
+
 #define system_has_cmpxchg128()		1
 
 static __always_inline u128 arch_cmpxchg128(volatile u128 *ptr, u128 old, u128 new)