KVM: x86: Remove return code from enable_irq/nmi_window

It's no longer possible to enter enable_irq_window in guest mode when
L1 intercepts external interrupts and we are entering L2. This is now
caught in vcpu_enter_guest. So we can remove the check from the VMX
version of enable_irq_window, thus the need to return an error code from
both enable_irq_window and enable_nmi_window.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -729,8 +729,8 @@ struct kvm_x86_ops {
 	int (*nmi_allowed)(struct kvm_vcpu *vcpu);
 	bool (*get_nmi_mask)(struct kvm_vcpu *vcpu);
 	void (*set_nmi_mask)(struct kvm_vcpu *vcpu, bool masked);
-	int (*enable_nmi_window)(struct kvm_vcpu *vcpu);
-	int (*enable_irq_window)(struct kvm_vcpu *vcpu);
+	void (*enable_nmi_window)(struct kvm_vcpu *vcpu);
+	void (*enable_irq_window)(struct kvm_vcpu *vcpu);
 	void (*update_cr8_intercept)(struct kvm_vcpu *vcpu, int tpr, int irr);
 	int (*vm_has_apicv)(struct kvm *kvm);
 	void (*hwapic_irr_update)(struct kvm_vcpu *vcpu, int max_irr);

arch/x86/kvm/svm.c

@@ -3650,7 +3650,7 @@ static int svm_interrupt_allowed(struct kvm_vcpu *vcpu)
 	return ret;
 }
 
-static int enable_irq_window(struct kvm_vcpu *vcpu)
+static void enable_irq_window(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
@@ -3664,16 +3664,15 @@ static int enable_irq_window(struct kvm_vcpu *vcpu)
 		svm_set_vintr(svm);
 		svm_inject_irq(svm, 0x0);
 	}
-	return 0;
 }
 
-static int enable_nmi_window(struct kvm_vcpu *vcpu)
+static void enable_nmi_window(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
 	if ((svm->vcpu.arch.hflags & (HF_NMI_MASK | HF_IRET_MASK))
 	    == HF_NMI_MASK)
-		return 0; /* IRET will cause a vm exit */
+		return; /* IRET will cause a vm exit */
 
 	/*
 	 * Something prevents NMI from been injected. Single step over possible
@@ -3682,7 +3681,6 @@ static int enable_nmi_window(struct kvm_vcpu *vcpu)
 	svm->nmi_singlestep = true;
 	svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
 	update_db_bp_intercept(vcpu);
-	return 0;
 }
 
 static int svm_set_tss_addr(struct kvm *kvm, unsigned int addr)

arch/x86/kvm/vmx.c

@@ -4514,39 +4514,28 @@ static bool nested_exit_on_nmi(struct kvm_vcpu *vcpu)
 		PIN_BASED_NMI_EXITING;
 }
 
-static int enable_irq_window(struct kvm_vcpu *vcpu)
+static void enable_irq_window(struct kvm_vcpu *vcpu)
 {
 	u32 cpu_based_vm_exec_control;
 
-	if (is_guest_mode(vcpu) && nested_exit_on_intr(vcpu))
-		/*
-		 * We get here if vmx_interrupt_allowed() said we can't
-		 * inject to L1 now because L2 must run. The caller will have
-		 * to make L2 exit right after entry, so we can inject to L1
-		 * more promptly.
-		 */
-		return -EBUSY;
-
 	cpu_based_vm_exec_control = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL);
 	cpu_based_vm_exec_control |= CPU_BASED_VIRTUAL_INTR_PENDING;
 	vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, cpu_based_vm_exec_control);
-	return 0;
 }
 
-static int enable_nmi_window(struct kvm_vcpu *vcpu)
+static void enable_nmi_window(struct kvm_vcpu *vcpu)
 {
 	u32 cpu_based_vm_exec_control;
 
-	if (!cpu_has_virtual_nmis())
-		return enable_irq_window(vcpu);
-
-	if (vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) & GUEST_INTR_STATE_STI)
-		return enable_irq_window(vcpu);
+	if (!cpu_has_virtual_nmis() ||
+	    vmcs_read32(GUEST_INTERRUPTIBILITY_INFO) & GUEST_INTR_STATE_STI) {
+		enable_irq_window(vcpu);
+		return;
+	}
 
 	cpu_based_vm_exec_control = vmcs_read32(CPU_BASED_VM_EXEC_CONTROL);
 	cpu_based_vm_exec_control |= CPU_BASED_VIRTUAL_NMI_PENDING;
 	vmcs_write32(CPU_BASED_VM_EXEC_CONTROL, cpu_based_vm_exec_control);
-	return 0;
 }
 
 static void vmx_inject_irq(struct kvm_vcpu *vcpu)

arch/x86/kvm/x86.c

@@ -5976,11 +5976,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 			req_immediate_exit = true;
 		/* enable NMI/IRQ window open exits if needed */
 		else if (vcpu->arch.nmi_pending)
-			req_immediate_exit =
-				kvm_x86_ops->enable_nmi_window(vcpu) != 0;
+			kvm_x86_ops->enable_nmi_window(vcpu);
 		else if (kvm_cpu_has_injectable_intr(vcpu) || req_int_win)
-			req_immediate_exit =
-				kvm_x86_ops->enable_irq_window(vcpu) != 0;
+			kvm_x86_ops->enable_irq_window(vcpu);
 
 		if (kvm_lapic_enabled(vcpu)) {
 			/*