On Fri, 8 Jul 2016 17:39:22 -0400 (EDT) Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > > > > @@ -10727,8 +10732,14 @@ static void nested_vmx_vmexit(struct > > > > > kvm_vcpu *vcpu, u32 exit_reason, > > > > > load_vmcs12_host_state(vcpu, vmcs12); > > > > > > > > > > - /* Update TSC_OFFSET if TSC was changed while L2 ran > > > > > */ > > > > > + /* Update any VMCS fields that might have changed > > > > > while L2 ran */ vmcs_write64(TSC_OFFSET, > > > > > vmx->nested.vmcs01_tsc_offset); > > > > > + if (vmx->hv_deadline_tsc == -1) > > > > > + vmcs_clear_bits(PIN_BASED_VM_EXEC_CONTROL, > > > > > + > > > > > PIN_BASED_VMX_PREEMPTION_TIMER); > > > > > + else > > > > > + vmcs_set_bits(PIN_BASED_VM_EXEC_CONTROL, > > > > > + > > > > > PIN_BASED_VMX_PREEMPTION_TIMER); > > > > > > > > Why do we need change the vmcs01 here? Per my understanding, the > > > > vmcs01 is not changed when the L2 guest is running thus the > > > > PIN_BASED_VM_EXEC_CONTROL should not be changed? > > > > > > This is the point where we are updating the vmcs01 after > > > exiting. If vmx->hv_deadline_tsc has changed (for example > > > because of a preemption > > > > Thanks for the explaination. I try to go through the code and still > > have one question. I'd describe below and hope get your input. > > > > When the L2 guest running while the VMX Preemption timer triggered, > > the vcpu_enter_guest() will trigger vmx_handle_exit(), with the CPU > > vmcs as vmcs02. On the vmx_handle_exit(), the > > nested_vmx_exit_handled() return false as the 1st patch did, thus > > the vmcs is not switched. The kvm_lapic_expired_hv_timer() will be > > called with vmcs02, instead of vmcs01. Is it something we wanted? I > > assume we should use vmcs01 there since we will clear the > > preemption timer VMCS bit there. > > Actually we want both. For whatever reason, the interrupt might not > cause a vmexit---for example if the L0 PPR is masking the LVTT vector. > In this case, we need to cancel the preemption timer in the vmcs02 > (done by kvm_lapic_expired_hv_timer) and keep running L2. On the next > vmexit, nested_vmx_vmexit will load the vmcs01 and clear the > preemption timer bit. Got it and thanks for clarification. --jyh > > Of course this is only theory until Wanpeng confirms that my patch > works for him. :) > > Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
