[PATCH 2/3] locking/atomic/x86: Introduce arch_try_cmpxchg64()

Uros Bizjak
2020-12-15T18:32:22Z

Add arch_try_cmpxchg64(), similar to arch_try_cmpxchg(), that
operates with 64 bit operands. This function provides the same
interface for 32 bit and 64 bit targets.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
arch/x86/include/asm/cmpxchg_32.h | 62 ++++++++++++++++++++++++++-----
arch/x86/include/asm/cmpxchg_64.h | 6 +++
2 files changed, 59 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index 0a7fe0321613..8dcde400244e 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -35,15 +35,6 @@ static inline void set_64bit(volatile u64 *ptr, u64 value)
: "memory");
}

-#ifdef CONFIG_X86_CMPXCHG64
-#define arch_cmpxchg64(ptr, o, n) \
- ((__typeof__(*(ptr)))__cmpxchg64((ptr), (unsigned long long)(o), \
- (unsigned long long)(n)))
-#define arch_cmpxchg64_local(ptr, o, n) \
- ((__typeof__(*(ptr)))__cmpxchg64_local((ptr), (unsigned long long)(o), \
- (unsigned long long)(n)))
-#endif
-
static inline u64 __cmpxchg64(volatile u64 *ptr, u64 old, u64 new)
{
u64 prev;
@@ -71,6 +62,39 @@ static inline u64 __cmpxchg64_local(volatile u64 *ptr, u64 old, u64 new)
}

#ifndef CONFIG_X86_CMPXCHG64
+#define arch_cmpxchg64(ptr, o, n) \
+ ((__typeof__(*(ptr)))__cmpxchg64((ptr), (unsigned long long)(o), \
+ (unsigned long long)(n)))
+#define arch_cmpxchg64_local(ptr, o, n) \
+ ((__typeof__(*(ptr)))__cmpxchg64_local((ptr), (unsigned long long)(o), \
+
+#define __raw_try_cmpxchg64(_ptr, _pold, _new, lock) \
+({ \
+ bool success; \
+ __typeof__(_ptr) _old = (__typeof__(_ptr))(_pold); \
+ __typeof__(*(_ptr)) __old = *_old; \
+ __typeof__(*(_ptr)) __new = (_new); \
+ asm volatile(lock "cmpxchg8b %1" \
+ CC_SET(z) \
+ : CC_OUT(z) (success), \
+ "+m" (*_ptr), \
+ "+A" (__old) \
+ : "b" ((unsigned int)__new), \
+ "c" ((unsigned int)(__new>>32)) \
+ : "memory"); \
+ if (unlikely(!success)) \
+ *_old = __old; \
+ likely(success); \
+})
+
+#define __try_cmpxchg64(ptr, pold, new) \
+ __raw_try_cmpxchg64((ptr), (pold), (new), LOCK_PREFIX)
+
+#define arch_try_cmpxchg64(ptr, pold, new) \
+ __try_cmpxchg64((ptr), (pold), (new))
+
+#else
+
/*
* Building a kernel capable running on 80386 and 80486. It may be necessary
* to simulate the cmpxchg8b on the 80386 and 80486 CPU.
@@ -108,6 +132,26 @@ static inline u64 __cmpxchg64_local(volatile u64 *ptr, u64 old, u64 new)
: "memory"); \
__ret; })

+#define arch_try_cmpxchg64(ptr, po, n) \
+({ \
+ bool success; \
+ __typeof__(ptr) _old = (__typeof__(ptr))(po); \
+ __typeof__(*(ptr)) __old = *_old; \
+ __typeof__(*(ptr)) __new = (n); \
+ alternative_io(LOCK_PREFIX_HERE \
+ "call cmpxchg8b_emu", \
+ "lock; cmpxchg8b (%%esi)" , \
+ X86_FEATURE_CX8, \
+ "+A" (__old), \
+ "S" ((ptr)), \
+ "b" ((unsigned int)__new), \
+ "c" ((unsigned int)(__new>>32)) \
+ : "memory"); \
+ success = (__old == *_old); \
+ if (unlikely(!success)) \
+ *_old = __old; \
+ likely(success); \
+})
#endif

#define system_has_cmpxchg_double() boot_cpu_has(X86_FEATURE_CX8)
diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
index 072e5459fe2f..250187ac8248 100644
--- a/arch/x86/include/asm/cmpxchg_64.h
+++ b/arch/x86/include/asm/cmpxchg_64.h
@@ -19,6 +19,12 @@ static inline void set_64bit(volatile u64 *ptr, u64 val)
arch_cmpxchg_local((ptr), (o), (n)); \
})

+#define arch_try_cmpxchg64(ptr, po, n) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ arch_try_cmpxchg((ptr), (po), (n)); \
+})
+
#define system_has_cmpxchg_double() boot_cpu_has(X86_FEATURE_CX16)

#endif /* _ASM_X86_CMPXCHG_64_H */
--
2.26.2