2017-06-12 23:08-0700, Wanpeng Li:
> From: Wanpeng Li <[email protected]>
> 
> Adds another flag bit (bit 2) to MSR_KVM_ASYNC_PF_EN. If bit 2 is 1, async 
> page faults are delivered to L1 as #PF vmexits; if bit 2 is 0, 
> kvm_can_do_async_pf 
> returns 0 if in guest mode.
> 
> Cc: Paolo Bonzini <[email protected]>
> Cc: Radim Krčmář <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---

I think KVM (L1) should also do something like

  diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
  index dd274db9bf77..c15a9f178e60 100644
  --- a/arch/x86/kvm/vmx.c
  +++ b/arch/x86/kvm/vmx.c
  @@ -7991,7 +7991,7 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu 
*vcpu)
                if (is_nmi(intr_info))
                        return false;
                else if (is_page_fault(intr_info))
  -                     return enable_ept;
  +                     return !vmx->apf_reason && enable_ept;
                else if (is_no_device(intr_info) &&
                         !(vmcs12->guest_cr0 & X86_CR0_TS))
                        return false;

so it doesn't pass the APF directed towards it (L1) into L2 if there is
L3 at the moment.

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