KVM: x86: nSVM: deal with L1 hypervisor that intercepts interrupts but lets L2 control them

Fix a corner case in which the L1 hypervisor intercepts
interrupts (INTERCEPT_INTR) and either doesn't set
virtual interrupt masking (V_INTR_MASKING) or enters a
nested guest with EFLAGS.IF disabled prior to the entry.

In this case, despite the fact that L1 intercepts the interrupts,
KVM still needs to set up an interrupt window to wait before
injecting the INTR vmexit.

Currently the KVM instead enters an endless loop of 'req_immediate_exit'.

Exactly the same issue also happens for SMIs and NMI.
Fix this as well.

Note that on VMX, this case is impossible as there is only
'vmexit on external interrupts' execution control which either set,
in which case both host and guest's EFLAGS.IF
are ignored, or not set, in which case no VMexits are delivered.
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220207155447.840194-8-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm/svm.c

@@ -3361,11 +3361,13 @@ static int svm_nmi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
 	if (svm->nested.nested_run_pending)
 		return -EBUSY;
 
+	if (svm_nmi_blocked(vcpu))
+		return 0;
+
 	/* An NMI must not be injected into L2 if it's supposed to VM-Exit.  */
 	if (for_injection && is_guest_mode(vcpu) && nested_exit_on_nmi(svm))
 		return -EBUSY;
-
-	return !svm_nmi_blocked(vcpu);
+	return 1;
 }
 
 static bool svm_get_nmi_mask(struct kvm_vcpu *vcpu)
@@ -3417,9 +3419,13 @@ bool svm_interrupt_blocked(struct kvm_vcpu *vcpu)
 static int svm_interrupt_allowed(struct kvm_vcpu *vcpu, bool for_injection)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
+
 	if (svm->nested.nested_run_pending)
 		return -EBUSY;
 
+	if (svm_interrupt_blocked(vcpu))
+		return 0;
+
 	/*
 	 * An IRQ must not be injected into L2 if it's supposed to VM-Exit,
 	 * e.g. if the IRQ arrived asynchronously after checking nested events.
@@ -3427,7 +3433,7 @@ static int svm_interrupt_allowed(struct kvm_vcpu *vcpu, bool for_injection)
 	if (for_injection && is_guest_mode(vcpu) && nested_exit_on_intr(svm))
 		return -EBUSY;
 
-	return !svm_interrupt_blocked(vcpu);
+	return 1;
 }
 
 static void svm_enable_irq_window(struct kvm_vcpu *vcpu)
@@ -4158,11 +4164,14 @@ static int svm_smi_allowed(struct kvm_vcpu *vcpu, bool for_injection)
 	if (svm->nested.nested_run_pending)
 		return -EBUSY;
 
+	if (svm_smi_blocked(vcpu))
+		return 0;
+
 	/* An SMI must not be injected into L2 if it's supposed to VM-Exit.  */
 	if (for_injection && is_guest_mode(vcpu) && nested_exit_on_smi(svm))
 		return -EBUSY;
 
-	return !svm_smi_blocked(vcpu);
+	return 1;
 }
 
 static int svm_enter_smm(struct kvm_vcpu *vcpu, char *smstate)