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Tue, 05 Nov 2019 02:23:15 -0800 (PST) X-Google-Smtp-Source: APXvYqybAnv9rx4J+dG+3zALibmvXj0MCS3vNaSu6P5s+2lri5gmcAcljRuafrbJ+2RXJymJ54T8bQ== X-Received: by 2002:a5d:6947:: with SMTP id r7mr3007044wrw.129.1572949395415; Tue, 05 Nov 2019 02:23:15 -0800 (PST) Received: from [192.168.10.150] ([93.56.166.5]) by smtp.gmail.com with ESMTPSA id 205sm20611901wmb.3.2019.11.05.02.23.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Nov 2019 02:23:14 -0800 (PST) Subject: Re: [PATCH 12/13] KVM: retpolines: x86: eliminate retpoline from svm.c exit handlers To: Andrea Arcangeli , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Vitaly Kuznetsov , Sean Christopherson References: <20191104230001.27774-1-aarcange@redhat.com> <20191104230001.27774-13-aarcange@redhat.com> From: Paolo Bonzini Openpgp: preference=signencrypt Message-ID: <5ed26dee-e439-6c2f-cd10-e73fefbd3a02@redhat.com> Date: Tue, 5 Nov 2019 11:21:03 +0100 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: <20191104230001.27774-13-aarcange@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 05/11/19 00:00, Andrea Arcangeli wrote: > It's enough to check the exit value and issue a direct call to avoid > the retpoline for all the common vmexit reasons. > > After this commit is applied, here the most common retpolines executed > under a high resolution timer workload in the guest on a SVM host: > > [..] > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_rax+33 > ktime_get_update_offsets_now+70 > hrtimer_interrupt+131 > smp_apic_timer_interrupt+106 > apic_timer_interrupt+15 > start_sw_timer+359 > restart_apic_timer+85 > kvm_set_msr_common+1497 > msr_interception+142 > vcpu_enter_guest+684 > kvm_arch_vcpu_ioctl_run+261 > kvm_vcpu_ioctl+559 > do_vfs_ioctl+164 > ksys_ioctl+96 > __x64_sys_ioctl+22 > do_syscall_64+89 > entry_SYSCALL_64_after_hwframe+68 > ]: 1940 > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_r12+33 > force_qs_rnp+217 > rcu_gp_kthread+1270 > kthread+268 > ret_from_fork+34 > ]: 4644 > @[]: 25095 > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_rax+33 > lapic_next_event+28 > clockevents_program_event+148 > hrtimer_start_range_ns+528 > start_sw_timer+356 > restart_apic_timer+85 > kvm_set_msr_common+1497 > msr_interception+142 > vcpu_enter_guest+684 > kvm_arch_vcpu_ioctl_run+261 > kvm_vcpu_ioctl+559 > do_vfs_ioctl+164 > ksys_ioctl+96 > __x64_sys_ioctl+22 > do_syscall_64+89 > entry_SYSCALL_64_after_hwframe+68 > ]: 41474 > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_rax+33 > clockevents_program_event+148 > hrtimer_start_range_ns+528 > start_sw_timer+356 > restart_apic_timer+85 > kvm_set_msr_common+1497 > msr_interception+142 > vcpu_enter_guest+684 > kvm_arch_vcpu_ioctl_run+261 > kvm_vcpu_ioctl+559 > do_vfs_ioctl+164 > ksys_ioctl+96 > __x64_sys_ioctl+22 > do_syscall_64+89 > entry_SYSCALL_64_after_hwframe+68 > ]: 41474 > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_rax+33 > ktime_get+58 > clockevents_program_event+84 > hrtimer_start_range_ns+528 > start_sw_timer+356 > restart_apic_timer+85 > kvm_set_msr_common+1497 > msr_interception+142 > vcpu_enter_guest+684 > kvm_arch_vcpu_ioctl_run+261 > kvm_vcpu_ioctl+559 > do_vfs_ioctl+164 > ksys_ioctl+96 > __x64_sys_ioctl+22 > do_syscall_64+89 > entry_SYSCALL_64_after_hwframe+68 > ]: 41887 > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_rax+33 > lapic_next_event+28 > clockevents_program_event+148 > hrtimer_try_to_cancel+168 > hrtimer_cancel+21 > kvm_set_lapic_tscdeadline_msr+43 > kvm_set_msr_common+1497 > msr_interception+142 > vcpu_enter_guest+684 > kvm_arch_vcpu_ioctl_run+261 > kvm_vcpu_ioctl+559 > do_vfs_ioctl+164 > ksys_ioctl+96 > __x64_sys_ioctl+22 > do_syscall_64+89 > entry_SYSCALL_64_after_hwframe+68 > ]: 42723 > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_rax+33 > clockevents_program_event+148 > hrtimer_try_to_cancel+168 > hrtimer_cancel+21 > kvm_set_lapic_tscdeadline_msr+43 > kvm_set_msr_common+1497 > msr_interception+142 > vcpu_enter_guest+684 > kvm_arch_vcpu_ioctl_run+261 > kvm_vcpu_ioctl+559 > do_vfs_ioctl+164 > ksys_ioctl+96 > __x64_sys_ioctl+22 > do_syscall_64+89 > entry_SYSCALL_64_after_hwframe+68 > ]: 42766 > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_rax+33 > ktime_get+58 > clockevents_program_event+84 > hrtimer_try_to_cancel+168 > hrtimer_cancel+21 > kvm_set_lapic_tscdeadline_msr+43 > kvm_set_msr_common+1497 > msr_interception+142 > vcpu_enter_guest+684 > kvm_arch_vcpu_ioctl_run+261 > kvm_vcpu_ioctl+559 > do_vfs_ioctl+164 > ksys_ioctl+96 > __x64_sys_ioctl+22 > do_syscall_64+89 > entry_SYSCALL_64_after_hwframe+68 > ]: 42848 > @[ > trace_retpoline+1 > __trace_retpoline+30 > __x86_indirect_thunk_rax+33 > ktime_get+58 > start_sw_timer+279 > restart_apic_timer+85 > kvm_set_msr_common+1497 > msr_interception+142 > vcpu_enter_guest+684 > kvm_arch_vcpu_ioctl_run+261 > kvm_vcpu_ioctl+559 > do_vfs_ioctl+164 > ksys_ioctl+96 > __x64_sys_ioctl+22 > do_syscall_64+89 > entry_SYSCALL_64_after_hwframe+68 > ]: 499845 > > @total: 1780243 > > SVM has no TSC based programmable preemption timer so it is invoking > ktime_get() frequently. > > Signed-off-by: Andrea Arcangeli > --- > arch/x86/kvm/svm.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > index 0021e11fd1fb..3942bca46740 100644 > --- a/arch/x86/kvm/svm.c > +++ b/arch/x86/kvm/svm.c > @@ -4995,6 +4995,18 @@ int kvm_x86_handle_exit(struct kvm_vcpu *vcpu) > return 0; > } > > +#ifdef CONFIG_RETPOLINE > + if (exit_code == SVM_EXIT_MSR) > + return msr_interception(svm); > + else if (exit_code == SVM_EXIT_VINTR) > + return interrupt_window_interception(svm); > + else if (exit_code == SVM_EXIT_INTR) > + return intr_interception(svm); > + else if (exit_code == SVM_EXIT_HLT) > + return halt_interception(svm); > + else if (exit_code == SVM_EXIT_NPF) > + return npf_interception(svm); > +#endif > return svm_exit_handlers[exit_code](svm); > } > > Queued, thanks (BTW, I still disagree about HLT exits but okay). Paolo