Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when L2 guest is running

From	Haozhong Zhang <haozhong.zhang@intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when L2 guest is running
Date	2016-07-06 10:10 +0200
Message-ID	<rRQ49-6FO-23@gated-at.bofh.it> (permalink)
References	<rRNpD-4Ya-9@gated-at.bofh.it> <rRNJ0-563-13@gated-at.bofh.it> <rROc1-5vh-11@gated-at.bofh.it> <rRPKO-6jE-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 07/06/16 09:46, Paolo Bonzini wrote:
> 
> 
> On 06/07/2016 08:05, Haozhong Zhang wrote:
> >> > 
> >> > Nested preemption timer is emulated by hrtimer, so it doesn't
> >> > influence vmcs02, why this is needed?
> > Nested (L2) preemption timer is not affected for sure, and this patch
> > is to fix another problem caused by using L1 preemption timer for L1
> > TSC deadline timer. When we use L1 VMX preemption timer for L1 TSC
> > deadline timer, we intend to use the pin-based exec config and the VMX
> > preemption timer value in vmcs01. However, when L2 guest is running,
> > vmcs02 is loaded as the current VMCS so that a different VMX
> > preemption timer config is used (i.e. VMX preemption timer is disabled
> > in prepare_vmcs02()). If we still use preemption timer for L1 TSC
> > deadline timer at this moment, then L1 TSC deadline timer will not be
> > able to be triggered when L2 guest is running.
> 
> The right fix then is to set the pin-based controls in prepare_vmcs02,
> based on vcpu->arch.hv_deadline_tsc.

Then KVM needs to distinguish L1 and L2 VMEXITs for preemption timer
(or does KVM already have this?). The current implementation which
uses a separate hrtimer for L2 preemption timer can easily distinguish
them.

Haozhong

Thread

[PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when L2 guest is running Haozhong Zhang <haozhong.zhang@intel.com> - 2016-07-06 07:20 +0200
  Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when  L2 guest is running Wanpeng Li <kernellwp@gmail.com> - 2016-07-06 07:40 +0200
    Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when  L2 guest is running Paolo Bonzini <pbonzini@redhat.com> - 2016-07-06 08:10 +0200
    Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when  L2 guest is running Haozhong Zhang <haozhong.zhang@intel.com> - 2016-07-06 08:10 +0200
      Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when  L2 guest is running Paolo Bonzini <pbonzini@redhat.com> - 2016-07-06 09:50 +0200
        Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when  L2 guest is running Haozhong Zhang <haozhong.zhang@intel.com> - 2016-07-06 10:10 +0200
          Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when  L2 guest is running Haozhong Zhang <haozhong.zhang@intel.com> - 2016-07-06 10:10 +0200
            Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when  L2 guest is running Paolo Bonzini <pbonzini@redhat.com> - 2016-07-06 10:20 +0200
              Re: [PATCH] KVM: VMX: switch to hrtimer for TSC deadline timer when  L2 guest is running Haozhong Zhang <haozhong.zhang@intel.com> - 2016-07-06 10:30 +0200

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