Use try_cmpxchg64 instead of cmpxchg64 (*ptr, old, new) != old in pi_try_set_control. cmpxchg returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg): b9: 88 44 24 60 mov %al,0x60(%rsp) bd: 48 89 c8 mov %rcx,%rax c0: c6 44 24 62 f2 movb $0xf2,0x62(%rsp) c5: 48 8b 74 24 60 mov 0x60(%rsp),%rsi ca: f0 49 0f b1 34 24 lock cmpxchg %rsi,(%r12) d0: 48 39 c1 cmp %rax,%rcx d3: 75 cf jne a4 <vmx_vcpu_pi_load+0xa4> patched: c1: 88 54 24 60 mov %dl,0x60(%rsp) c5: c6 44 24 62 f2 movb $0xf2,0x62(%rsp) ca: 48 8b 54 24 60 mov 0x60(%rsp),%rdx cf: f0 48 0f b1 13 lock cmpxchg %rdx,(%rbx) d4: 75 d5 jne ab <vmx_vcpu_pi_load+0xab> Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Sean Christopherson <seanjc@xxxxxxxxxx> Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Cc: Wanpeng Li <wanpengli@xxxxxxxxxxx> Cc: Jim Mattson <jmattson@xxxxxxxxxx> Cc: Joerg Roedel <joro@xxxxxxxxxx> --- v2: - use address of local variable &old The patch is agains tip tree. --- arch/x86/kvm/vmx/posted_intr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c index 3834bb30ce54..259315ea5e44 100644 --- a/arch/x86/kvm/vmx/posted_intr.c +++ b/arch/x86/kvm/vmx/posted_intr.c @@ -42,7 +42,7 @@ static int pi_try_set_control(struct pi_desc *pi_desc, u64 old, u64 new) * update must be retried with a fresh snapshot an ON change causes * the cmpxchg to fail. */ - if (cmpxchg64(&pi_desc->control, old, new) != old) + if (!try_cmpxchg64(&pi_desc->control, &old, new)) return -EBUSY; return 0; -- 2.35.3
