Re: [PATCH 4/4] KVM: async_pf: Let host know whether the guest support delivery async_pf as #PF vmexit

Radim Krčmář
2017-06-13T18:19:24Z

2017-06-12 23:08-0700, Wanpeng Li:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> 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 <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---

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.