linux-kernel - Re: [PATCH] kvm: x86: fix a race condition result to lost INIT

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Message-ID: <CANRm+Czo0ZPf8kDKxGmCEjUfH6PH9E2NV3c_f8GkhryVR=rU5A@mail.gmail.com>
Date:   Sun, 30 Jul 2017 19:09:18 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Peng Hao <peng.hao2@....com.cn>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        kvm <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kvm: x86: fix a race condition result to lost INIT

2017-07-30 18:42 GMT+08:00  <peng.hao2@....com.cn>:
>> 2017-07-31 0:24 GMT+08:00 Peng Hao <peng.hao2@....com.cn>:
>
>> > when SMP VM start, AP may lost INIT because of receiving INIT between
>> > kvm_vcpu_ioctl_x86_get/set_vcpu_events.
>> >
>> >    vcpu 0                             vcpu 1
>> >                                kvm_vcpu_ioctl_x86_get_vcpu_events
>> >                                        events->smi.latched_init=0
>> >  send INIT to vcpu1
>> >    set vcpu1's pending_events
>> >                                kvm_vcpu_ioctl_x86_set_vcpu_events
>> >                                     events->smi.latched_init == 0
>> >                                       clear INIT in pending_events
>> > I don't think it need set/clear kernel state according to userspace's
>> > info.
>> >
>> > Signed-off-by: Peng Hao <peng.hao2@....com.cn>
>> > ---
>> >  arch/x86/kvm/x86.c | 6 ------
>> >  1 file changed, 6 deletions(-)
>> >
>> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> > index 6c7266f..393a7b7 100644
>> > --- a/arch/x86/kvm/x86.c
>> > +++ b/arch/x86/kvm/x86.c
>> > @@ -3157,12 +3157,6 @@ static int
>> > kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
>> >                         vcpu->arch.hflags |= HF_SMM_INSIDE_NMI_MASK;
>> >                 else
>> >                         vcpu->arch.hflags &= ~HF_SMM_INSIDE_NMI_MASK;
>> > -               if (lapic_in_kernel(vcpu)) {
>> > -                       if (events->smi.latched_init)
>> > -                               set_bit(KVM_APIC_INIT,
>> > &vcpu->arch.apic->pending_events);
>
>> This is not correct, you will lose the INIT after live migration. I
>> just send out another patch to fix it. Thanks for the report.
>
> yes, you're right. I should modify on qemu not kernel.

There is a patch here to fix it in kvm, https://lkml.org/lkml/2017/7/30/72

Regards,
Wanpeng Li

>
>> > -                       else
>> > -                               clear_bit(KVM_APIC_INIT,
>> > &vcpu->arch.apic->pending_events);
>> > -               }
>> >         }
>
>
>