linux-kernel - Re: [PATCH v3] KVM: LAPIC: Fix reentrancy issues with preempt notifiers

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Date:   Tue, 25 Jul 2017 15:44:09 +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 v3] KVM: LAPIC: Fix reentrancy issues with preempt notifiers

2017-07-25 15:25 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
> On 25/07/2017 00:43, Wanpeng Li wrote:
>> -     WARN_ON(!apic->lapic_timer.hv_timer_in_use);
>> +     preempt_disable();
>> +     /* The preempt notifier has called apic_timer_expired already */
>> +     if (!apic->lapic_timer.hv_timer_in_use)
>> +             goto out;
>>       WARN_ON(swait_active(&vcpu->wq));
>>       cancel_hv_timer(apic);
>>       apic_timer_expired(apic);
>> +out:
>> +     preempt_enable();
>
> If apic_timer_expired was called, and the timer is in periodic mode, it
> has already set the hv timer.  Should the out label be really at the end
> of the function, after the timer is restarted?  Otherwise you can call
> advance_periodic_timer_expiration twice.

I just send out v4 to fix it. Thanks for the review.

Regards,
Wanpeng Li

>
> Thanks,
>
> Paolo
>
>>
>>       if (apic_lvtt_period(apic) && apic->lapic_timer.period) {
>>               advance_periodic_target_expiration(apic);
>> @@ -1582,9 +1588,11 @@ void kvm_lapic_switch_to_sw_timer(struct kvm_vcpu *vcpu)
>>  {
>>       struct kvm_lapic *apic = vcpu->arch.apic;
>>
>> +     preempt_disable();
>>       /* Possibly the TSC deadline timer is not enabled yet */
>>       if (apic->lapic_timer.hv_timer_in_use)
>>               start_sw_timer(apic);
>> +     preempt_enable();
>>  }
>>  EXPORT_SYMBOL_GPL(kvm_lapic_switch_to_sw_timer);
>