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

[Wanpeng Li]

2016-07-07 16:10 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>:
>
>
> On 07/07/2016 05:46, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>>
>> 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".

Regards,
Wanpeng Li