KVM: x86: Refactor kvm_vcpu_do_singlestep() to remove out param

Return the single-step emulation result directly instead of via an out
param.  Presumably at some point in the past kvm_vcpu_do_singlestep()
could be called with *r==EMULATE_USER_EXIT, but that is no longer the
case, i.e. all callers are happy to overwrite their own return variable.
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -6474,7 +6474,7 @@ static int kvm_vcpu_check_hw_bp(unsigned long addr, u32 type, u32 dr7,
 	return dr6;
 }
 
-static void kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu, int *r)
+static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu)
 {
 	struct kvm_run *kvm_run = vcpu->run;
 
@@ -6483,10 +6483,10 @@ static void kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu, int *r)
 		kvm_run->debug.arch.pc = vcpu->arch.singlestep_rip;
 		kvm_run->debug.arch.exception = DB_VECTOR;
 		kvm_run->exit_reason = KVM_EXIT_DEBUG;
-		*r = EMULATE_USER_EXIT;
-	} else {
-		kvm_queue_exception_p(vcpu, DB_VECTOR, DR6_BS);
+		return EMULATE_USER_EXIT;
 	}
+	kvm_queue_exception_p(vcpu, DB_VECTOR, DR6_BS);
+	return EMULATE_DONE;
 }
 
 int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
@@ -6507,7 +6507,7 @@ int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
 	 * that sets the TF flag".
 	 */
 	if (unlikely(rflags & X86_EFLAGS_TF))
-		kvm_vcpu_do_singlestep(vcpu, &r);
+		r = kvm_vcpu_do_singlestep(vcpu);
 	return r == EMULATE_DONE;
 }
 EXPORT_SYMBOL_GPL(kvm_skip_emulated_instruction);
@@ -6720,7 +6720,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 		    exception_type(ctxt->exception.vector) == EXCPT_TRAP) {
 			kvm_rip_write(vcpu, ctxt->eip);
 			if (r == EMULATE_DONE && ctxt->tf)
-				kvm_vcpu_do_singlestep(vcpu, &r);
+				r = kvm_vcpu_do_singlestep(vcpu);
 			__kvm_set_rflags(vcpu, ctxt->eflags);
 		}