Re: [PATCH] KVM: X86: Fix loss of pending INIT due to race

[Paolo Bonzini]

On 30/07/2017 11:42, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng...@hotmail.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 not touching INIT pending if INIT is not latched 
> which in SMM and just restoring the latched INIT after SET_VCPU_EVENTS.
> 
> Thanks Peng Hao for the report and original commit message.
> 
> Reported-by: Peng Hao <peng.h...@zte.com.cn>
> Cc: Paolo Bonzini <pbonz...@redhat.com>
> Cc: Radim Krčmář <rkrc...@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng...@hotmail.com>
> ---
>  arch/x86/kvm/x86.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 1a4c84d..eaca86d 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3164,12 +3164,8 @@ 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);
> -                     else
> -                             clear_bit(KVM_APIC_INIT, 
> &vcpu->arch.apic->pending_events);
> -             }
> +             if (events->smi.latched_init && lapic_in_kernel(vcpu))
> +                     set_bit(KVM_APIC_INIT, 
> &vcpu->arch.apic->pending_events);

All this block:

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

only applies if you're in SMM, so perhaps you can move it under

        if (events->smi.smm)

?

Paolo

>       }
>  
>       kvm_make_request(KVM_REQ_EVENT, vcpu);
>