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18286883e7
Use atomic_try_cmpxchg() instead of atomic_cmpxchg(*ptr, old, new) == old in hv_nmi_unknown(). On x86 the CMPXCHG instruction returns success in the ZF flag, so this change saves a compare after CMPXCHG. The generated asm code improves from: 3e: 65 8b 15 00 00 00 00 mov %gs:0x0(%rip),%edx 45: b8 ff ff ff ff mov $0xffffffff,%eax 4a: f0 0f b1 15 00 00 00 lock cmpxchg %edx,0x0(%rip) 51: 00 52: 83 f8 ff cmp $0xffffffff,%eax 55: 0f 95 c0 setne %al to: 3e: 65 8b 15 00 00 00 00 mov %gs:0x0(%rip),%edx 45: b8 ff ff ff ff mov $0xffffffff,%eax 4a: f0 0f b1 15 00 00 00 lock cmpxchg %edx,0x0(%rip) 51: 00 52: 0f 95 c0 setne %al No functional change intended. Cc: "K. Y. Srinivasan" <kys@microsoft.com> Cc: Haiyang Zhang <haiyangz@microsoft.com> Cc: Wei Liu <wei.liu@kernel.org> Cc: Dexuan Cui <decui@microsoft.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Reviewed-by: Michael Kelley <mhklinux@outlook.com> Link: https://lore.kernel.org/r/20231114170038.381634-1-ubizjak@gmail.com Signed-off-by: Wei Liu <wei.liu@kernel.org> Message-ID: <20231114170038.381634-1-ubizjak@gmail.com> |
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