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

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Date:   Sun, 30 Jul 2017 17:44:47 +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

2017-07-31 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.

Regards,
Wanpeng Li

> -                       else
> -                               clear_bit(KVM_APIC_INIT, &vcpu->arch.apic->pending_events);
> -               }
>         }
>
>         kvm_make_request(KVM_REQ_EVENT, vcpu);
> --
> 1.8.3.1
>
>