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

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Date:   Sat, 27 May 2017 06:07:13 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH] KVM: X86: Fix preempt the preemption timer cancel

2017-05-26 23:57 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>
>
> 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