linux-kernel - Re: [PATCH v2] KVM: X86: Fix loss of pending INIT due to race

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Message-ID: <117b7114-eeb0-2074-f287-ed5bafae18a2@redhat.com>
Date:   Wed, 2 Aug 2017 09:44:27 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v2] KVM: X86: Fix loss of pending INIT due to race

On 02/08/2017 01:05, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@...mail.com>
> 
> 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
>                                       if (events->smi.latched_init == 0)
>                                         clear INIT in pending_events
> 
> This patch fixes it by just update SMM related flags if we are in SMM.
> 
> Thanks Peng Hao for the report and original commit message.
> 
> Reported-by: Peng Hao <peng.hao2@....com.cn>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Radim Krčmář <rkrcmar@...hat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
> ---
> v1 -> v2:
>  * move the stuff under if (events->smi_smm)
> 
>  arch/x86/kvm/x86.c | 19 +++++++++++--------
>  1 file changed, 11 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1a4c84d..839b5dad6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3160,15 +3160,18 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
>  		kvm_set_hflags(vcpu, hflags);
>  
>  		vcpu->arch.smi_pending = events->smi.pending;
> -		if (events->smi.smm_inside_nmi)
> -			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);
> +
> +		if (events->smi.smm) {
> +			if (events->smi.smm_inside_nmi)
> +				vcpu->arch.hflags |= HF_SMM_INSIDE_NMI_MASK;
>  			else
> -				clear_bit(KVM_APIC_INIT, &vcpu->arch.apic->pending_events);
> +				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);
> +				else
> +					clear_bit(KVM_APIC_INIT, &vcpu->arch.apic->pending_events);
> +			}
>  		}
>  	}
>  
> 


Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>