KVM: x86: Handle emulation failure directly in kvm_task_switch()

Consolidate the reporting of emulation failure into kvm_task_switch()
so that it can return EMULATE_USER_EXIT.  This helps pave the way for
removing EMULATE_FAIL altogether.

This also fixes a theoretical bug where task switch interception could
suppress an EMULATE_USER_EXIT return.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/svm.c

@@ -3892,17 +3892,10 @@ static int task_switch_interception(struct vcpu_svm *svm)
 	if (int_type != SVM_EXITINTINFO_TYPE_SOFT)
 		int_vec = -1;
 
-	if (kvm_task_switch(&svm->vcpu, tss_selector, int_vec, reason,
-				has_error_code, error_code) == EMULATE_FAIL)
-		goto fail;
 
-	return 1;
 
-fail:
-	svm->vcpu.run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
-	svm->vcpu.run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
-	svm->vcpu.run->internal.ndata = 0;
-	return 0;
+	return kvm_task_switch(&svm->vcpu, tss_selector, int_vec, reason,
+			       has_error_code, error_code) != EMULATE_USER_EXIT;
 }
 
 static int cpuid_interception(struct vcpu_svm *svm)

arch/x86/kvm/vmx/vmx.c

@@ -5074,21 +5074,13 @@ static int handle_task_switch(struct kvm_vcpu *vcpu)
 		       type != INTR_TYPE_NMI_INTR))
 		skip_emulated_instruction(vcpu);
 
-	if (kvm_task_switch(vcpu, tss_selector,
-			    type == INTR_TYPE_SOFT_INTR ? idt_index : -1, reason,
-			    has_error_code, error_code) == EMULATE_FAIL) {
-		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
-		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
-		vcpu->run->internal.ndata = 0;
-		return 0;
-	}
-
 	/*
 	 * TODO: What about debug traps on tss switch?
 	 *       Are we supposed to inject them and update dr6?
 	 */
-
-	return 1;
+	return kvm_task_switch(vcpu, tss_selector,
+			       type == INTR_TYPE_SOFT_INTR ? idt_index : -1,
+			       reason, has_error_code, error_code) != EMULATE_USER_EXIT;
 }
 
 static int handle_ept_violation(struct kvm_vcpu *vcpu)

arch/x86/kvm/x86.c

@@ -8693,9 +8693,12 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index,
 
 	ret = emulator_task_switch(ctxt, tss_selector, idt_index, reason,
 				   has_error_code, error_code);
-
-	if (ret)
-		return EMULATE_FAIL;
+	if (ret) {
+		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+		vcpu->run->internal.ndata = 0;
+		return EMULATE_USER_EXIT;
+	}
 
 	kvm_rip_write(vcpu, ctxt->eip);
 	kvm_set_rflags(vcpu, ctxt->eflags);