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 <aarcange@xxxxxxxxxx> > --- > 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
