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

[Haozhong Zhang]

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