Re: [PATCH] KVM: X86: Fix preempt the preemption timer cancel

From: Wanpeng Li
Date: Fri May 26 2017 - 21:18:42 EST


2017-05-26 23:57 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>:
>
>
> On 21/05/2017 05:32, Wanpeng Li wrote:
>> CPU0 CPU1
>>
>> vmx_cancel_hv_timer
>> vCPU0's vmx->hv_deadline_tsc = -1
>>
>> preempt occur
>>
>> clear preemption timer field in CPU1's active vmcs
>> vCPU0's apic_timer.hv_timer_in_use = false
>> vmx_vcpu_run(vCPU0)
>> vmx_arm_hv_timer
>> if (vmx->hv_deadline_tsc == -1)
>> nothing change
>>
>> handle_preemption_timer(vCPU0)
>> kvm_lapic_expired_hv_timer
>> WARN_ON(!apic->lapic_timer.hv_timer_in_use);
>
>
> I think it's more like this, what do you think?
>
> CPU0 CPU1
>
> preemption timer vmexit
> handle_preemption_timer(vCPU0)
> kvm_lapic_expired_hv_timer
> vmx_cancel_hv_timer
> vmx->hv_deadline_tsc = -1
> vmcs_clear_bits
> /* hv_timer_in_use still true */
> sched_out
> sched_in
> kvm_arch_vcpu_load
> vmx_set_hv_timer
> write vmx->hv_deadline_tsc
> vmcs_set_bits
> /* back in kvm_lapic_expired_hv_timer */
> hv_timer_in_use = false
> ...
> vmx_vcpu_run
> vmx_arm_hv_run
> write preemption timer deadline
> spurious preemption timer vmexit
> handle_preemption_timer(vCPU0)
> kvm_lapic_expired_hv_timer
> WARN_ON(!apic->lapic_timer.hv_timer_in_use);

Looks good to me, thanks for your help, Paolo. :)

Regards,
Wanpeng Li