linux-kernel - Re: [PATCH v3 2/4] KVM: X86: Fix loss of exception which has not yet injected

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Message-ID: <CANRm+CzRS6enhr2Wh6M+1yNxgKROzPJ2d7p5gz4BumgH2Djfug@mail.gmail.com>
Date:   Thu, 24 Aug 2017 17:34:31 +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 2/4] KVM: X86: Fix loss of exception which has not yet injected

2017-08-24 17:13 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
> 2017-08-24 16:57 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
>> On 24/08/2017 08:52, Wanpeng Li wrote:
>>>> @@ -6862,6 +6876,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>>>>                                 kvm_x86_ops->enable_nmi_window(vcpu);
>>>>                         if (kvm_cpu_has_injectable_intr(vcpu) || req_int_win)
>>>>                                 kvm_x86_ops->enable_irq_window(vcpu);
>>>> +                       WARN_ON(vcpu->arch.exception.pending);
>>>
>>> This WARN_ON() is suggested during the review of last version,
>>> however, there are many cases in inject_pending_event() can result in
>>> return directly w/ vcpu->arch.exception.pending is true. Actually I
>>> have already catched the warning several times during the testing. I
>>> think we should remove it when committing.
>>
>> No, it's a good thing that it's failing, because it's finding a bug.
>> There's no such thing as an "exception window", so at the very least it
>
> Good point, the code looks good, I will fold it in next version.
> However, I still can observe the warning.
>
> Regards,
> Wanpeng Li

I observed sometimes both vcpu->arch.exception.pending and
vcpu->arch.expception.injected are true before executing below codes:

if (vcpu->arch.exception.injected) {
    kvm_x86_ops->queue_exception(vcpu);
    return 0;
}

Regards,
Wanpeng Li

>
>> should set req_immediate_exit to true.
>>
>> Does this help?
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index b698b2f135a2..76d5a192be6c 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -6365,14 +6365,20 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
>>                 return 0;
>>         }
>>
>> -       if (vcpu->arch.nmi_injected) {
>> -               kvm_x86_ops->set_nmi(vcpu);
>> -               return 0;
>> -       }
>> +       /*
>> +        * Exceptions must be injected immediately, or the exception
>> +        * frame will have the address of the NMI or interrupt handler.
>> +        */
>> +       if (!vcpu->arch.exception.pending) {
>> +               if (vcpu->arch.nmi_injected) {
>> +                       kvm_x86_ops->set_nmi(vcpu);
>> +                       return 0;
>> +               }
>>
>> -       if (vcpu->arch.interrupt.pending) {
>> -               kvm_x86_ops->set_irq(vcpu);
>> -               return 0;
>> +               if (vcpu->arch.interrupt.pending) {
>> +                       kvm_x86_ops->set_irq(vcpu);
>> +                       return 0;
>> +               }
>>         }
>>
>>         if (is_guest_mode(vcpu) && kvm_x86_ops->check_nested_events) {
>>
>> Paolo