@@ -572,6 +572,7 @@ The following vCPU events do not need to be enabled or disabled,
 because these are sent as a result of certain commands::
 
 	KVMI_EVENT_PAUSE_VCPU
+	KVMI_EVENT_SINGLESTEP
 	KVMI_EVENT_TRAP
 
 However, the events mentioned above can be disallowed.

@@ -980,8 +981,12 @@ Enables/disables singlestep for the selected vCPU.
 The introspection tool should use *KVMI_GET_VERSION*, to check
 if the hardware supports singlestep (see **KVMI_GET_VERSION**).
 
+After every instruction, a *KVMI_EVENT_SINGLESTEP* event is sent
+to the introspection tool.
+
 :Errors:
 
+* -KVM_EPERM  - the *KVMI_EVENT_SINGLESTEP* event is disallowed
 * -KVM_EOPNOTSUPP - the hardware doesn't support singlestep
 * -KVM_EINVAL - the padding is not zero
 * -KVM_EAGAIN - the selected vCPU can't be introspected yet

@@ -1375,3 +1380,30 @@ The *CONTINUE* action will continue the page fault handling via emulation.
 The *RETRY* action is used by the introspection tool to retry the
 execution of the current instruction, usually because it changed the
 instruction pointer or the page restrictions.
+
+11. KVMI_EVENT_SINGLESTEP
+-------------------------
+
+:Architectures: x86
+:Versions: >= 1
+:Actions: CONTINUE, CRASH
+:Parameters:
+
+::
+
+	struct kvmi_event;
+
+:Returns:
+
+::
+
+	struct kvmi_vcpu_hdr;
+	struct kvmi_event_reply;
+	struct kvmi_event_singlestep {
+		__u8 failed;
+		__u8 padding[7];
+	};
+
+This event is sent when the current instruction has been executed or
+failed and the singlestep has been enabled for the selected vCPU
+(see **KVMI_VCPU_CONTROL_SINGLESTEP**).

@@ -5464,6 +5464,7 @@ static int handle_invalid_op(struct kvm_vcpu *vcpu)
 
 static int handle_monitor_trap(struct kvm_vcpu *vcpu)
 {
+	kvmi_singlestep_done(vcpu);
 	return 1;
 }
 

@@ -6025,6 +6026,11 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu,
 		return 1;
 	}
 
+	if (kvmi_vcpu_running_singlestep(vcpu) &&
+	    exit_reason != EXIT_REASON_EPT_VIOLATION &&
+	    exit_reason != EXIT_REASON_MONITOR_TRAP_FLAG)
+		kvmi_singlestep_failed(vcpu);
+
 	if (exit_reason >= kvm_vmx_max_exit_handlers)
 		goto unexpected_vmexit;
 #ifdef CONFIG_RETPOLINE

@@ -95,6 +95,8 @@ bool kvmi_hypercall_event(struct kvm_vcpu *vcpu);
 bool kvmi_breakpoint_event(struct kvm_vcpu *vcpu, u64 gva, u8 insn_len);
 bool kvmi_enter_guest(struct kvm_vcpu *vcpu);
 bool kvmi_vcpu_running_singlestep(struct kvm_vcpu *vcpu);
+void kvmi_singlestep_done(struct kvm_vcpu *vcpu);
+void kvmi_singlestep_failed(struct kvm_vcpu *vcpu);
 
 #else
 

@@ -113,6 +115,8 @@ static inline bool kvmi_enter_guest(struct kvm_vcpu *vcpu)
 			{ return true; }
 static inline bool kvmi_vcpu_running_singlestep(struct kvm_vcpu *vcpu)
 			{ return false; }
+static inline void kvmi_singlestep_done(struct kvm_vcpu *vcpu) { }
+static inline void kvmi_singlestep_failed(struct kvm_vcpu *vcpu) { }
 
 #endif /* CONFIG_KVM_INTROSPECTION */
 

@@ -58,6 +58,7 @@ enum {
 	KVMI_EVENT_DESCRIPTOR = 7,
 	KVMI_EVENT_MSR        = 8,
 	KVMI_EVENT_PF         = 9,
+	KVMI_EVENT_SINGLESTEP = 10,
 
 	KVMI_NUM_EVENTS
 };

@@ -209,4 +210,9 @@ struct kvmi_event_pf {
 	__u32 padding3;
 };
 
+struct kvmi_event_singlestep {
+	__u8 failed;
+	__u8 padding[7];
+};
+
 #endif /* _UAPI__LINUX_KVMI_H */

@@ -745,6 +745,14 @@ static void stop_vcpu_worker(pthread_t vcpu_thread,
 	wait_vcpu_worker(vcpu_thread);
 }
 
+static int __do_vcpu_command(struct kvm_vm *vm, int cmd_id,
+			     struct kvmi_msg_hdr *req, size_t req_size,
+			     void *rpl, size_t rpl_size)
+{
+	send_message(cmd_id, req, req_size);
+	return receive_cmd_reply(req, rpl, rpl_size);
+}
+
 static int do_vcpu_command(struct kvm_vm *vm, int cmd_id,
 			   struct kvmi_msg_hdr *req, size_t req_size,
 			   void *rpl, size_t rpl_size)

@@ -755,13 +763,24 @@ static int do_vcpu_command(struct kvm_vm *vm, int cmd_id,
 
 	vcpu_thread = start_vcpu_worker(&data);
 
-	send_message(cmd_id, req, req_size);
-	r = receive_cmd_reply(req, rpl, rpl_size);
+	r = __do_vcpu_command(vm, cmd_id, req, req_size, rpl, rpl_size);
 
 	stop_vcpu_worker(vcpu_thread, &data);
 	return r;
 }
 
+static int __do_vcpu0_command(struct kvm_vm *vm, int cmd_id,
+			      struct kvmi_msg_hdr *req, size_t req_size,
+			      void *rpl, size_t rpl_size)
+{
+	struct kvmi_vcpu_hdr *vcpu_hdr = (struct kvmi_vcpu_hdr *)req;
+
+	vcpu_hdr->vcpu = 0;
+
+	send_message(cmd_id, req, req_size);
+	return receive_cmd_reply(req, rpl, rpl_size);
+}
+
 static int do_vcpu0_command(struct kvm_vm *vm, int cmd_id,
 			    struct kvmi_msg_hdr *req, size_t req_size,
 			    void *rpl, size_t rpl_size)

@@ -1668,26 +1687,69 @@ static void test_event_pf(struct kvm_vm *vm)
 	test_pf(vm, cbk_test_event_pf);
 }
 
-static void test_cmd_vcpu_control_singlestep(struct kvm_vm *vm)
+static void control_singlestep(struct kvm_vm *vm, bool enable)
 {
 	struct {
 		struct kvmi_msg_hdr hdr;
 		struct kvmi_vcpu_hdr vcpu_hdr;
 		struct kvmi_vcpu_control_singlestep cmd;
 	} req = {};
+	int r;
+
+	req.cmd.enable = enable;
+	r = __do_vcpu0_command(vm, KVMI_VCPU_CONTROL_SINGLESTEP,
+			       &req.hdr, sizeof(req), NULL, 0);
+	TEST_ASSERT(r == 0,
+		"KVMI_VCPU_CONTROL_SINGLESTEP failed, error %d (%s)\n",
+		-r, kvm_strerror(-r));
+}
+
+static void enable_singlestep(struct kvm_vm *vm)
+{
+	control_singlestep(vm, true);
+}
+
+static void disable_singlestep(struct kvm_vm *vm)
+{
+	control_singlestep(vm, false);
+}
+
+static void test_cmd_vcpu_control_singlestep(struct kvm_vm *vm)
+{
+	struct vcpu_worker_data data = { .vm = vm, .vcpu_id = VCPU_ID };
+	struct {
+		struct kvmi_event common;
+		struct kvmi_event_singlestep singlestep;
+	} ev;
+	__u16 event_id = KVMI_EVENT_SINGLESTEP;
+	struct vcpu_reply rpl = {};
+	struct kvmi_msg_hdr hdr;
+	pthread_t vcpu_thread;
 
 	if (!features.singlestep) {
 		DEBUG("Skip %s()\n", __func__);
 		return;
 	}
 
-	req.cmd.enable = true;
-	test_vcpu0_command(vm, KVMI_VCPU_CONTROL_SINGLESTEP,
-			   &req.hdr, sizeof(req), NULL, 0);
+	enable_vcpu_event(vm, event_id);
 
-	req.cmd.enable = false;
-	test_vcpu0_command(vm, KVMI_VCPU_CONTROL_SINGLESTEP,
-			   &req.hdr, sizeof(req), NULL, 0);
+	vcpu_thread = start_vcpu_worker(&data);
+
+	enable_singlestep(vm);
+
+	receive_event(&hdr, &ev.common, sizeof(ev), event_id);
+
+	DEBUG("SINGLESTEP event, rip 0x%llx success %d\n",
+		ev.common.arch.regs.rip, !ev.singlestep.failed);
+
+	disable_singlestep(vm);
+
+	reply_to_event(&hdr, &ev.common, KVMI_EVENT_ACTION_CONTINUE,
+			&rpl, sizeof(rpl));
+
+	stop_vcpu_worker(vcpu_thread, &data);
+
+	disable_vcpu_event(vm, KVMI_EVENT_SINGLESTEP);
 }
 
 static void test_introspection(struct kvm_vm *vm)

@@ -110,6 +110,7 @@ static void setup_known_events(void)
 	set_bit(KVMI_EVENT_MSR, Kvmi_known_vcpu_events);
 	set_bit(KVMI_EVENT_PAUSE_VCPU, Kvmi_known_vcpu_events);
 	set_bit(KVMI_EVENT_PF, Kvmi_known_vcpu_events);
+	set_bit(KVMI_EVENT_SINGLESTEP, Kvmi_known_vcpu_events);
 	set_bit(KVMI_EVENT_TRAP, Kvmi_known_vcpu_events);
 	set_bit(KVMI_EVENT_XSETBV, Kvmi_known_vcpu_events);
 

@@ -1320,3 +1321,63 @@ bool kvmi_vcpu_running_singlestep(struct kvm_vcpu *vcpu)
 	return ret;
 }
 EXPORT_SYMBOL(kvmi_vcpu_running_singlestep);
+
+static u32 kvmi_send_singlestep(struct kvm_vcpu *vcpu, bool success)
+{
+	struct kvmi_event_singlestep e;
+	int err, action;
+
+	memset(&e, 0, sizeof(e));
+	e.failed = success ? 0 : 1;
+
+	err = kvmi_send_event(vcpu, KVMI_EVENT_SINGLESTEP, &e, sizeof(e),
+			      NULL, 0, &action);
+	if (err)
+		return KVMI_EVENT_ACTION_CONTINUE;
+
+	return action;
+}
+
+static void kvmi_singlestep_event(struct kvm_vcpu *vcpu, bool success)
+{
+	u32 action;
+
+	action = kvmi_send_singlestep(vcpu, success);
+	switch (action) {
+	case KVMI_EVENT_ACTION_CONTINUE:
+		break;
+	default:
+		kvmi_handle_common_event_actions(vcpu->kvm, action,
+						"SINGLESTEP");
+	}
+}
+
+static void kvmi_handle_singlestep_exit(struct kvm_vcpu *vcpu, bool success)
+{
+	struct kvm_vcpu_introspection *vcpui;
+	struct kvm_introspection *kvmi;
+	struct kvm *kvm = vcpu->kvm;
+
+	kvmi = kvmi_get(kvm);
+	if (!kvmi)
+		return;
+
+	vcpui = VCPUI(vcpu);
+
+	if (vcpui->singlestep.loop)
+		kvmi_singlestep_event(vcpu, success);
+
+	kvmi_put(kvm);
+}
+
+void kvmi_singlestep_done(struct kvm_vcpu *vcpu)
+{
+	kvmi_handle_singlestep_exit(vcpu, true);
+}
+EXPORT_SYMBOL(kvmi_singlestep_done);
+
+void kvmi_singlestep_failed(struct kvm_vcpu *vcpu)
+{
+	kvmi_handle_singlestep_exit(vcpu, false);
+}
+EXPORT_SYMBOL(kvmi_singlestep_failed);

@@ -630,6 +630,11 @@ static int handle_vcpu_control_singlestep(const struct kvmi_vcpu_cmd_job *job,
 	bool done;
 	int i;
 
+	if (!is_event_allowed(KVMI(vcpu->kvm), KVMI_EVENT_SINGLESTEP)) {
+		ec = -KVM_EPERM;
+		goto reply;
+	}
+
 	for (i = 0; i < sizeof(req->padding); i++)
 		if (req->padding[i])
 			goto reply;