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Re: [PATCH v3 2/2] KVM: nVMX: Fix preemption timer bit set in vmcs02 even if L1 doesn't enable it

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2016-07-07 18:33 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> On 07/07/2016 10:31, Wanpeng Li wrote:
>> 2016-07-07 16:10 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>>>
>>>
>>> On 07/07/2016 05:46, Wanpeng Li wrote:
>>>> From: Wanpeng Li <wanpeng.li@hotmail.com>
>>>>
>>>> We will go to vcpu_run() loop after L0 emulates VMRESUME which incurs
>>>> kvm_sched_out and kvm_sched_in operations since cond_resched() will be
>>>> called once need resched. Preemption timer will be reprogrammed if vCPU
>>>> is scheduled to a different pCPU. Then the preemption timer bit of vmcs02
>>>> will be set if L0 enable preemption timer to run L1 even if L1 doesn't
>>>> enable preemption timer to run L2.
>>>>
>>>> This patch fix it by don't reprogram preemption timer of vmcs02 if L1's
>>>> vCPU is scheduled on diffent pCPU when we are in the way to vmresume
>>>> nested guest.
>>>
>>> Again, this is wrong.  There is no reason why L1's APIC timer cannot be
>>> emulated through the vmcs12's preemption timer setting.  The only issue
>>> is getting the pin-based execution controls right.
>>
>> This patch doesn't intend to implement "L1 TSC deadline timer to
>> trigger while L2 is running", it just solves why vmcs02 is set even if
>>
>> exec_control = vmcs12->pin_based_vm_exec_control;
>> exec_control |= vmcs_config.pin_based_exec_ctrl;
>> exec_control &= ~PIN_BASED_VMX_PREEMPTION_TIMER;
>>
>> We should set pin-based execution controls right to implement "L1 TSC
>> deadline timer to trigger while L2 is running".
>
> Ok, now I get it, but I still cannot understand the logic in your patch.
>
> You write:
>
>                 if (!is_guest_mode(vcpu) &&
>                         kvm_lapic_hv_timer_in_use(vcpu) &&
>                                 kvm_x86_ops->set_hv_timer(vcpu,
>                                         kvm_get_lapic_tscdeadline_msr(vcpu)))
>                         kvm_lapic_switch_to_sw_timer(vcpu);
>
> but this means that while L2 runs you miss L1's APIC timer interrupt.  Do you
> want this instead:
>
>                 if (kvm_lapic_hv_timer_in_use(vcpu) &&
>                     (is_guest_mode(vcpu) ||
>                      kvm_x86_ops->set_hv_timer(vcpu,
>                                                kvm_get_lapic_tscdeadline_msr(vcpu))))
>                         kvm_lapic_switch_to_sw_timer(vcpu);

Nice point out. :) I will send out another version.

Regards,
Wanpeng Li

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[PATCH v3 1/2] KVM: nVMX: Fix incorrect preemption timer vmexit in nested guest Wanpeng Li <kernellwp@gmail.com> - 2016-07-07 05:50 +0200
  [PATCH v3 2/2] KVM: nVMX: Fix preemption timer bit set in vmcs02 even if L1 doesn't enable it Wanpeng Li <kernellwp@gmail.com> - 2016-07-07 05:50 +0200
    Re: [PATCH v3 2/2] KVM: nVMX: Fix preemption timer bit set in vmcs02  even if L1 doesn't enable it Paolo Bonzini <pbonzini@redhat.com> - 2016-07-07 10:20 +0200
      Re: [PATCH v3 2/2] KVM: nVMX: Fix preemption timer bit set in vmcs02  even if L1 doesn't enable it Wanpeng Li <kernellwp@gmail.com> - 2016-07-07 10:40 +0200
        Re: [PATCH v3 2/2] KVM: nVMX: Fix preemption timer bit set in vmcs02  even if L1 doesn't enable it Paolo Bonzini <pbonzini@redhat.com> - 2016-07-07 12:40 +0200
          Re: [PATCH v3 2/2] KVM: nVMX: Fix preemption timer bit set in vmcs02  even if L1 doesn't enable it Wanpeng Li <kernellwp@gmail.com> - 2016-07-07 13:00 +0200
  Re: [PATCH v3 1/2] KVM: nVMX: Fix incorrect preemption timer vmexit  in nested guest Haozhong Zhang <haozhong.zhang@intel.com> - 2016-07-07 08:50 +0200
    Re: [PATCH v3 1/2] KVM: nVMX: Fix incorrect preemption timer vmexit  in nested guest Wanpeng Li <kernellwp@gmail.com> - 2016-07-07 09:00 +0200
      Re: [PATCH v3 1/2] KVM: nVMX: Fix incorrect preemption timer vmexit  in nested guest Haozhong Zhang <haozhong.zhang@intel.com> - 2016-07-07 09:10 +0200
        Re: [PATCH v3 1/2] KVM: nVMX: Fix incorrect preemption timer vmexit  in nested guest Wanpeng Li <kernellwp@gmail.com> - 2016-07-07 09:10 +0200
          Re: [PATCH v3 1/2] KVM: nVMX: Fix incorrect preemption timer vmexit  in nested guest Haozhong Zhang <haozhong.zhang@intel.com> - 2016-07-07 09:30 +0200

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