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| author | Uros Bizjak <ubizjak@gmail.com> | 2024-04-08 12:13:58 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2024-04-09 10:51:03 +0300 |
| commit | aef95dac9ce4f271cc43195ffc175114ed934cbe (patch) | |
| tree | f94e5309223aa88569dc21294d4542240a4d9eb5 | |
| parent | 7016cc5def44b9dcb28089efae4412fa0d6c78c2 (diff) | |
| download | linux-aef95dac9ce4f271cc43195ffc175114ed934cbe.tar.xz | |
locking/atomic/x86: Introduce arch_try_cmpxchg64() for !CONFIG_X86_CMPXCHG64
Commit:
6d12c8d308e68 ("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
| -rw-r--r-- | arch/x86/include/asm/cmpxchg_32.h | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h index fe40d0681ea8..9e0d330dd5d0 100644 --- a/arch/x86/include/asm/cmpxchg_32.h +++ b/arch/x86/include/asm/cmpxchg_32.h @@ -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) |