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/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)