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([2001:b07:6468:f312:9520:22e6:6416:5c36]) by smtp.gmail.com with ESMTPSA id c1sm8310783wmk.20.2019.09.23.02.57.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Sep 2019 02:57:58 -0700 (PDT) Subject: Re: [PATCH 15/17] KVM: retpolines: x86: eliminate retpoline from vmx.c exit handlers To: Vitaly Kuznetsov , Andrea Arcangeli Cc: "Dr. David Alan Gilbert" , Marcelo Tosatti , Peter Xu , kvm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190920212509.2578-1-aarcange@redhat.com> <20190920212509.2578-16-aarcange@redhat.com> <87o8zb8ik1.fsf@vitty.brq.redhat.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <7329012d-0b3b-ce86-f58d-3d2d5dc5a790@redhat.com> Date: Mon, 23 Sep 2019 11:57:57 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <87o8zb8ik1.fsf@vitty.brq.redhat.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 23/09/19 11:31, Vitaly Kuznetsov wrote: > +#ifdef CONFIG_RETPOLINE > + if (exit_reason == EXIT_REASON_MSR_WRITE) > + return handle_wrmsr(vcpu); > + else if (exit_reason == EXIT_REASON_PREEMPTION_TIMER) > + return handle_preemption_timer(vcpu); > + else if (exit_reason == EXIT_REASON_PENDING_INTERRUPT) > + return handle_interrupt_window(vcpu); > + else if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT) > + return handle_external_interrupt(vcpu); > + else if (exit_reason == EXIT_REASON_HLT) > + return handle_halt(vcpu); > + else if (exit_reason == EXIT_REASON_PAUSE_INSTRUCTION) > + return handle_pause(vcpu); > + else if (exit_reason == EXIT_REASON_MSR_READ) > + return handle_rdmsr(vcpu); > + else if (exit_reason == EXIT_REASON_CPUID) > + return handle_cpuid(vcpu); > + else if (exit_reason == EXIT_REASON_EPT_MISCONFIG) > + return handle_ept_misconfig(vcpu); > +#endif > return kvm_vmx_exit_handlers[exit_reason](vcpu); Most of these, while frequent, are already part of slow paths. I would keep only EXIT_REASON_MSR_WRITE, EXIT_REASON_PREEMPTION_TIMER, EXIT_REASON_EPT_MISCONFIG and add EXIT_REASON_IO_INSTRUCTION. If you make kvm_vmx_exit_handlers const, can the compiler substitute for instance kvm_vmx_exit_handlers[EXIT_REASON_MSR_WRITE] with handle_wrmsr? Just thinking out loud, not sure if it's an improvement code-wise. Paolo Paolo