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+CxQuLnsiTkhGPiU4fF-JK52CY_n1oOeAsv+8LvTfsKqzA@mail.gmail.com>
Date:   Thu, 24 Aug 2017 17:13:31 +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 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

> 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