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

From	Paolo Bonzini <pbonzini@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3 2/2] KVM: nVMX: Fix preemption timer bit set in vmcs02 even if L1 doesn't enable it
Date	2016-07-07 10:20 +0200
Message-ID	<rScHp-4lY-65@gated-at.bofh.it> (permalink)
References	<rS8u5-1rw-1@gated-at.bofh.it> <rS8u5-1rw-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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.

Paolo

Thread

[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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