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([2001:b07:6468:f312:f43b:97b2:4c89:7446]) by smtp.gmail.com with ESMTPSA id v7sm3846697wmg.3.2020.04.21.04.40.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Apr 2020 04:40:07 -0700 (PDT) Subject: Re: [PATCH 2/2] KVM: VMX: Handle preemption timer fastpath To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , Haiwei Li References: <1587468026-15753-1-git-send-email-wanpengli@tencent.com> <1587468026-15753-3-git-send-email-wanpengli@tencent.com> From: Paolo Bonzini Message-ID: <68eb0e46-4c2a-0292-3dfa-db2ae2b2b13d@redhat.com> Date: Tue, 21 Apr 2020 13:40:06 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <1587468026-15753-3-git-send-email-wanpengli@tencent.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/04/20 13:20, Wanpeng Li wrote: > + > + if (!vmx->req_immediate_exit && > + !unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) { > + if (!vmx_interrupt_allowed(vcpu) || > + !apic_lvtt_tscdeadline(apic) || > + vmx->rmode.vm86_active || > + is_smm(vcpu) || > + !kvm_apic_hw_enabled(apic)) > + return EXIT_FASTPATH_NONE; > + > + if (!apic->lapic_timer.hv_timer_in_use) > + return EXIT_FASTPATH_CONT_RUN; > + > + WARN_ON(swait_active(&vcpu->wq)); > + vmx_cancel_hv_timer(vcpu); > + apic->lapic_timer.hv_timer_in_use = false; > + > + if (atomic_read(&apic->lapic_timer.pending)) > + return EXIT_FASTPATH_CONT_RUN; > + > + ktimer->expired_tscdeadline = ktimer->tscdeadline; > + vmx_fast_deliver_interrupt(vcpu); > + ktimer->tscdeadline = 0; > + return EXIT_FASTPATH_CONT_RUN; > + } > + Can you explain all the checks you have here, and why you need something more complex than apic_timer_expired (possibly by adding some optimizations to kvm_apic_local_deliver)? This code is impossible to maintain. Paolo