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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id i11sm3631994wrs.10.2020.02.06.02.47.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 06 Feb 2020 02:47:03 -0800 (PST) From: Vitaly Kuznetsov To: linmiaohe Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, pbonzini@redhat.com, rkrcmar@redhat.com, sean.j.christopherson@intel.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com Subject: Re: [PATCH] KVM: apic: reuse smp_wmb() in kvm_make_request() In-Reply-To: <1580954375-5030-1-git-send-email-linmiaohe@huawei.com> References: <1580954375-5030-1-git-send-email-linmiaohe@huawei.com> Date: Thu, 06 Feb 2020 11:47:02 +0100 Message-ID: <87d0asgfh5.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org linmiaohe writes: > From: Miaohe Lin > > There is already an smp_mb() barrier in kvm_make_request(). We reuse it > here. > > Signed-off-by: Miaohe Lin > --- > arch/x86/kvm/lapic.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index eafc631d305c..ea871206a370 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -1080,9 +1080,12 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode, > result = 1; > /* assumes that there are only KVM_APIC_INIT/SIPI */ > apic->pending_events = (1UL << KVM_APIC_INIT); > - /* make sure pending_events is visible before sending > - * the request */ > - smp_wmb(); > + /* > + * Make sure pending_events is visible before sending > + * the request. > + * There is already an smp_wmb() in kvm_make_request(), > + * we reuse that barrier here. > + */ Let me suggest an alternative wording, "kvm_make_request() provides smp_wmb() so pending_events changes are guaranteed to be visible" But there is nothing wrong with yours, it's just longer than it could be :-) Reviewed-by: Vitaly Kuznetsov > kvm_make_request(KVM_REQ_EVENT, vcpu); > kvm_vcpu_kick(vcpu); > } -- Vitaly