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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id e11sm6590628pfn.49.2021.08.27.07.58.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Aug 2021 07:58:38 -0700 (PDT) Date: Fri, 27 Aug 2021 14:58:35 +0000 From: Sean Christopherson To: Peter Zijlstra Cc: Will Deacon , Mark Rutland , Ingo Molnar , Arnaldo Carvalho de Melo , Catalin Marinas , Marc Zyngier , Guo Ren , Nick Hu , Greentime Hu , Vincent Chen , Paul Walmsley , Palmer Dabbelt , Albert Ou , Thomas Gleixner , Borislav Petkov , x86@kernel.org, Paolo Bonzini , Boris Ostrovsky , Juergen Gross , Alexander Shishkin , Jiri Olsa , Namhyung Kim , James Morse , Alexandru Elisei , Suzuki K Poulose , "H. Peter Anvin" , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Stefano Stabellini , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-csky@vger.kernel.org, linux-riscv@lists.infradead.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, Artem Kashkanov , Like Xu , Zhu Lingshan Subject: Re: [PATCH 07/15] KVM: Use dedicated flag to track if KVM is handling an NMI from guest Message-ID: References: <20210827005718.585190-1-seanjc@google.com> <20210827005718.585190-8-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org On Fri, Aug 27, 2021, Peter Zijlstra wrote: > On Thu, Aug 26, 2021 at 05:57:10PM -0700, Sean Christopherson wrote: > > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h > > index 5cedc0e8a5d5..4c5ba4128b38 100644 > > --- a/arch/x86/kvm/x86.h > > +++ b/arch/x86/kvm/x86.h > > @@ -395,9 +395,10 @@ static inline void kvm_unregister_perf_callbacks(void) > > > > DECLARE_PER_CPU(struct kvm_vcpu *, current_vcpu); > > > > -static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu) > > +static inline void kvm_before_interrupt(struct kvm_vcpu *vcpu, bool is_nmi) > > { > > __this_cpu_write(current_vcpu, vcpu); > > + WRITE_ONCE(vcpu->arch.handling_nmi_from_guest, is_nmi); > > > > kvm_register_perf_callbacks(); > > } > > @@ -406,6 +407,7 @@ static inline void kvm_after_interrupt(struct kvm_vcpu *vcpu) > > { > > kvm_unregister_perf_callbacks(); > > > > + WRITE_ONCE(vcpu->arch.handling_nmi_from_guest, false); > > __this_cpu_write(current_vcpu, NULL); > > } > > Does this rely on kvm_{,un}register_perf_callback() being a function > call and thus implying a sequence point to order the stores? No, I'm just terrible at remembering which macros provide what ordering guarantees, i.e. I was thinking WRITE_ONCE provided guarantees against compiler reordering.