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locking/atomic/x86: Introduce arch_try_cmpxchg64() for !CONFIG_X86_CMPXCHG64

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Commit:

  6d12c8d308 ("percpu: Wire up cmpxchg128")

improved emulated cmpxchg8b_emu() library function to return
success/failure in a ZF flag.

Define arch_try_cmpxchg64() for !CONFIG_X86_CMPXCHG64 targets
to override the generic archy_try_cmpxchg() with an optimized
target specific implementation that handles ZF flag.

The assembly code at the call sites improves from:

   bf56d:	e8 fc ff ff ff       	call   cmpxchg8b_emu
   bf572:	8b 74 24 28          	mov    0x28(%esp),%esi
   bf576:	89 c3                	mov    %eax,%ebx
   bf578:	89 d1                	mov    %edx,%ecx
   bf57a:	8b 7c 24 2c          	mov    0x2c(%esp),%edi
   bf57e:	89 f0                	mov    %esi,%eax
   bf580:	89 fa                	mov    %edi,%edx
   bf582:	31 d8                	xor    %ebx,%eax
   bf584:	31 ca                	xor    %ecx,%edx
   bf586:	09 d0                	or     %edx,%eax
   bf588:	0f 84 e3 01 00 00    	je     bf771 <...>

to:

   bf572:	e8 fc ff ff ff       	call   cmpxchg8b_emu
   bf577:	0f 84 b6 01 00 00    	je     bf733 <...>

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20240408091547.90111-4-ubizjak@gmail.com
This commit is contained in:
Uros Bizjak
2024-04-08 11:13:58 +02:00
committed by Ingo Molnar
parent 7016cc5def
commit aef95dac9c
1 changed files with 28 additions and 0 deletions
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arch/x86/include/asm/cmpxchg_32.h
+28
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@@ -122,6 +122,34 @@ static __always_inline u64 arch_cmpxchg64_local(volatile u64 *ptr, u64 old, u64
}
#define arch_cmpxchg64_local arch_cmpxchg64_local
#define __arch_try_cmpxchg64_emu(_ptr, _oldp, _new) \
({ \
union __u64_halves o = { .full = *(_oldp), }, \
n = { .full = (_new), }; \
bool ret; \
\
asm volatile(ALTERNATIVE(LOCK_PREFIX_HERE \
"call cmpxchg8b_emu", \
"lock; cmpxchg8b %[ptr]", X86_FEATURE_CX8) \
CC_SET(e) \
: CC_OUT(e) (ret), \
[ptr] "+m" (*(_ptr)), \
"+a" (o.low), "+d" (o.high) \
: "b" (n.low), "c" (n.high), "S" (_ptr) \
: "memory"); \
\
if (unlikely(!ret)) \
*(_oldp) = o.full; \
\
likely(ret); \
})
static __always_inline bool arch_try_cmpxchg64(volatile u64 *ptr, u64 *oldp, u64 new)
{
return __arch_try_cmpxchg64_emu(ptr, oldp, new);
}
#define arch_try_cmpxchg64 arch_try_cmpxchg64
#endif
#define system_has_cmpxchg64() boot_cpu_has(X86_FEATURE_CX8)