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[93.103.18.160]) by smtp.gmail.com with ESMTPSA id s27-20020a170906221b00b006f3ef214e73sm954490ejs.217.2022.05.18.06.46.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 May 2022 06:46:10 -0700 (PDT) From: Uros Bizjak To: kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Paolo Bonzini , Sean Christopherson Subject: [PATCH] KVM: VMX: Use try_cmpxchg64 in pi_try_set_control Date: Wed, 18 May 2022 15:45:50 +0200 Message-Id: <20220518134550.2358-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.35.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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 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 Cc: Paolo Bonzini Cc: Sean Christopherson Signed-off-by: Uros Bizjak Reported-by: kernel test robot Reported-by: kernel test robot --- Patch requires commits 0aa7be05d83cc584da0782405e8007e351dfb6cc and c2df0a6af177b6c06a859806a876f92b072dc624 from tip.git --- arch/x86/kvm/vmx/posted_intr.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/kvm/vmx/posted_intr.c b/arch/x86/kvm/vmx/posted_intr.c index 3834bb30ce54..4d41d5994a26 100644 --- a/arch/x86/kvm/vmx/posted_intr.c +++ b/arch/x86/kvm/vmx/posted_intr.c @@ -34,7 +34,7 @@ static inline struct pi_desc *vcpu_to_pi_desc(struct kvm_vcpu *vcpu) return &(to_vmx(vcpu)->pi_desc); } -static int pi_try_set_control(struct pi_desc *pi_desc, u64 old, u64 new) +static int pi_try_set_control(struct pi_desc *pi_desc, u64 *pold, u64 new) { /* * PID.ON can be set at any time by a different vCPU or by hardware, @@ -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, pold, new)) return -EBUSY; return 0; @@ -111,7 +111,7 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu) * descriptor was modified on "put" to use the wakeup vector. */ new.nv = POSTED_INTR_VECTOR; - } while (pi_try_set_control(pi_desc, old.control, new.control)); + } while (pi_try_set_control(pi_desc, &old.control, new.control)); local_irq_restore(flags); @@ -161,7 +161,7 @@ static void pi_enable_wakeup_handler(struct kvm_vcpu *vcpu) /* set 'NV' to 'wakeup vector' */ new.nv = POSTED_INTR_WAKEUP_VECTOR; - } while (pi_try_set_control(pi_desc, old.control, new.control)); + } while (pi_try_set_control(pi_desc, &old.control, new.control)); /* * Send a wakeup IPI to this CPU if an interrupt may have been posted