Re: [PATCH] KVM: VMX: Fix losing blocking by NMI in the guest interruptibility-state field

[Paolo Bonzini]

On 14/07/2017 11:39, Wanpeng Li wrote:
> However, commit 0be9c7a89f750 (KVM: VMX: set "blocked by NMI" flag if EPT 
> violation happens during IRET from NMI) just fixes the fault due to EPT violation. 
> This patch tries to fix the fault due to the page fault of shadow page table. 
> 
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
>  arch/x86/kvm/vmx.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 84e62ac..32ca063 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5709,6 +5709,11 @@ static int handle_exception(struct kvm_vcpu *vcpu)
>  	}
>  
>  	if (is_page_fault(intr_info)) {
> +
> +		if (!(to_vmx(vcpu)->idt_vectoring_info & VECTORING_INFO_VALID_MASK) &&
> +			(intr_info & INTR_INFO_UNBLOCK_NMI))
> +			vmcs_set_bits(GUEST_INTERRUPTIBILITY_INFO, GUEST_INTR_STATE_NMI);
> +
>  		cr2 = vmcs_readl(EXIT_QUALIFICATION);
>  		/* EPT won't cause page fault directly */
>  		WARN_ON_ONCE(!vcpu->arch.apf.host_apf_reason && enable_ept);

vmx_recover_nmi_blocking is supposed to do the same.  EPT and PML-full exits
need separate code because they store bit 12 in the exit qualification rather
than the VM-exit interruption info.  I think the bug is in the handling of
vmx->nmi_known_unmasked. 

The following patch fixes it for me, can you test it too?

Thanks,

Paolo

--------- 8< -------------------
From: Paolo Bonzini <pbonzini@xxxxxxxxxx
Subject: [PATCH] KVM: nVMX: track NMI blocking state separately for each VMCS

vmx_recover_nmi_blocking is using a cached value of the guest 
interruptibility info, which is stored in vmx->nmi_known_unmasked.
vmx_recover_nmi_blocking is run for both normal and nested guests,
so the cached value must be per-VMCS.

This fixes eventinj.flat in a nested non-EPT environment.  With EPT it 
works, because the EPT violation handler doesn't have the 
vmx->nmi_known_unmasked optimization (it is unnecessary because, unlike 
vmx_recover_nmi_blocking, it can just look at the exit qualification).

Thanks to Wanpeng Li for debugging the testcase and providing an initial
patch.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>


diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 32db3f5dce7f..504df356a10c 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -198,7 +198,8 @@ struct loaded_vmcs {
 	struct vmcs *vmcs;
 	struct vmcs *shadow_vmcs;
 	int cpu;
-	int launched;
+	bool launched;
+	bool nmi_known_unmasked;
 	struct list_head loaded_vmcss_on_cpu_link;
 };
 
@@ -5497,10 +5498,8 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
-	if (!is_guest_mode(vcpu)) {
-		++vcpu->stat.nmi_injections;
-		vmx->nmi_known_unmasked = false;
-	}
+	++vcpu->stat.nmi_injections;
+	vmx->loaded_vmcs->nmi_known_unmasked = false;
 
 	if (vmx->rmode.vm86_active) {
 		if (kvm_inject_realmode_interrupt(vcpu, NMI_VECTOR, 0) != EMULATE_DONE)
@@ -5514,16 +5513,21 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
 
 static bool vmx_get_nmi_mask(struct kvm_vcpu *vcpu)
 {
-	if (to_vmx(vcpu)->nmi_known_unmasked)
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	bool masked;
+
+	if (vmx->loaded_vmcs->nmi_known_unmasked)
 		return false;
-	return vmcs_read32(GUEST_INTERRUPTIBILITY_INFO)	& GUEST_INTR_STATE_NMI;
+	masked = vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) & GUEST_INTR_STATE_NMI;
+	vmx->loaded_vmcs->nmi_known_unmasked = !masked;
+	return masked;
 }
 
 static void vmx_set_nmi_mask(struct kvm_vcpu *vcpu, bool masked)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
-	vmx->nmi_known_unmasked = !masked;
+	vmx->loaded_vmcs->nmi_known_unmasked = !masked;
 	if (masked)
 		vmcs_set_bits(GUEST_INTERRUPTIBILITY_INFO,
 			      GUEST_INTR_STATE_NMI);
@@ -8719,7 +8723,7 @@ static void vmx_recover_nmi_blocking(struct vcpu_vmx *vmx)
 
 	idtv_info_valid = vmx->idt_vectoring_info & VECTORING_INFO_VALID_MASK;
 
-	if (vmx->nmi_known_unmasked)
+	if (vmx->loaded_vmcs->nmi_known_unmasked)
 		return;
 	/*
 	 * Can't use vmx->exit_intr_info since we're not sure what
@@ -8743,7 +8747,7 @@ static void vmx_recover_nmi_blocking(struct vcpu_vmx *vmx)
 		vmcs_set_bits(GUEST_INTERRUPTIBILITY_INFO,
 			      GUEST_INTR_STATE_NMI);
 	else
-		vmx->nmi_known_unmasked =
+		vmx->loaded_vmcs->nmi_known_unmasked =
 			!(vmcs_read32(GUEST_INTERRUPTIBILITY_INFO)
 			  & GUEST_INTR_STATE_NMI);
 }