wakeup-from-suspend and system_wakeup changes

When issuing the qmp/hmp 'system_wakeup' command, what happens in a nutshell is:

- qmp_system_wakeup_request set runstate to RUNNING, sets a wakeup_reason and notify the event
- in the main_loop, all vcpus are paused, a system reset is issued, all subscribers of wakeup_notifiers receives a notification, vcpus are then resumed and the wake up QAPI event is fired

Note that this procedure alone doesn't ensure that the guest will awake from SUSPENDED state - the subscribers of the wake up event must take action to resume the guest, otherwise the guest will simply reboot. At this moment, only the ACPI machines via acpi_pm1_cnt_init and xen_hvm_init have wake-up from suspend support.

However, only the presence of 'system_wakeup' is required for QGA to support 'guest-suspend-ram' and 'guest-suspend-hybrid' at this moment. This means that the user/management will expect to suspend the guest using one of those suspend commands and then resume execution using system_wakeup, regardless of the support offered in system_wakeup in the first place.

This patch creates a new API called query-current-machine [1], that holds a new flag called 'wakeup-suspend-support' that indicates if the guest supports wake up from suspend via system_wakeup. The machine is considered to implement wake-up support if a call to a new 'qemu_register_wakeup_support' is made during its init, as it is now being done inside acpi_pm1_cnt_init and xen_hvm_init. This allows for any other machine type to declare wake-up support regardless of ACPI state or wakeup_notifiers subscription, making easier for newer implementations that might have their own mechanisms in the future.

This is the expected output of query-current-machine when running a x86 guest:

{"execute" : "query-current-machine"}
{"return": {"wakeup-suspend-support": true}}

Running the same x86 guest, but with the --no-acpi option:

{"execute" : "query-current-machine"}
{"return": {"wakeup-suspend-support": false}}

This is the output when running a pseries guest:

{"execute" : "query-current-machine"}
{"return": {"wakeup-suspend-support": false}}

With this extra tool, management can avoid situations where a guest that does not have proper suspend/wake capabilities ends up in inconsistent state (e.g.
https://github.com/open-power-host-os/qemu/issues/31).

[1] the decision of creating the query-current-machine API is based on discussions in the QEMU mailing list where it was decided that query-target wasn't a proper place to store the wake-up flag, neither was query-machines because this isn't a static property of the machine object. This new API can then be used to store other dynamic machine properties that are scattered around the code ATM. More info at:
https://lists.gnu.org/archive/html/qemu-devel/2018-05/msg04235.html

Reported-by Balamuruhan S <[email protected]>

Signed-off-by Daniel Henrique Barboza <[email protected]>

This patch updates the descriptions of 'guest-suspend-ram' and 'guest-suspend-hybrid' to mention that both commands relies now on the proper support for wake up from suspend, retrieved by the 'wakeup-suspend-support' attribute of the 'query-current-machine' QMP command.

Reported-by Balamuruhan S <[email protected]>

Signed-off-by Daniel Henrique Barboza <[email protected]>

Reviewed-by Michael Roth <[email protected]>

The qmp/hmp command 'system_wakeup' is simply a direct call to 'qemu_system_wakeup_request' from vl.c. This function verifies if runstate is SUSPENDED and if the wake up reason is valid before proceeding. However, no error or warning is thrown if any of those pre-requirements isn't met. There is no way for the caller to differentiate between a successful wakeup or an error state caused when trying to wake up a guest that wasn't suspended.

This means that system_wakeup is silently failing, which can be considered a bug. Adding error handling isn't an API break in this case - applications that didn't check the result will remain broken, the ones that check it will have a chance to deal with it.

Adding to that, the commit before previous created a new QMP API called query-current-machine, with a new flag called wakeup-suspend-support, that indicates if the guest has the capability of waking up from suspended state. Although such guest will never reach SUSPENDED state and erroring it out in this scenario would suffice, it is more informative for the user to differentiate between a failure because the guest isn't suspended versus a failure because the guest does not have support for wake up at all.

All this considered, this patch changes qmp_system_wakeup to check if the guest is capable of waking up from suspend, and if it is suspended. After this patch, this is the output of system_wakeup in a guest that does not have wake-up from suspend support (ppc64):

(qemu) system_wakeup
wake-up from suspend is not supported by this guest (qemu)

And this is the output of system_wakeup in a x86 guest that has the support but isn't suspended:

(qemu) system_wakeup
Unable to wake up: guest is not in suspended state (qemu)

Reported-by Balamuruhan S <[email protected]>

Signed-off-by Daniel Henrique Barboza <[email protected]>

changes in v11:
- fixed typos, changed version to 4.0 in patches 1 and 3
- changed text in patch 2 to be less alarming
- patch 3: changed error handling
- previous version link:
http://lists.nongnu.org/archive/html/qemu-devel/2018-11/msg01774.html

Quoted 6 lines · Daniel Henrique Barboza

changes in v11:
- fixed typos, changed version to 4.0 in patches 1 and 3
- changed text in patch 2 to be less alarming
- patch 3: changed error handling
- previous version link:
http://lists.nongnu.org/archive/html/qemu-devel/2018-11/msg01774.html

Looks ready to me. Who's going to merge it?

The qmp/hmp command 'system_wakeup' is simply a direct call to 'qemu_system_wakeup_request' from vl.c. This function verifies if runstate is SUSPENDED and if the wake up reason is valid before proceeding. However, no error or warning is thrown if any of those pre-requirements isn't met. There is no way for the caller to differentiate between a successful wakeup or an error state caused when trying to wake up a guest that wasn't suspended.

This means that system_wakeup is silently failing, which can be considered a bug. Adding error handling isn't an API break in this case - applications that didn't check the result will remain broken, the ones that check it will have a chance to deal with it.

Adding to that, the commit before previous created a new QMP API called query-current-machine, with a new flag called wakeup-suspend-support, that indicates if the guest has the capability of waking up from suspended state. Although such guest will never reach SUSPENDED state and erroring it out in this scenario would suffice, it is more informative for the user to differentiate between a failure because the guest isn't suspended versus a failure because the guest does not have support for wake up at all.

All this considered, this patch changes qmp_system_wakeup to check if the guest is capable of waking up from suspend, and if it is suspended. After this patch, this is the output of system_wakeup in a guest that does not have wake-up from suspend support (ppc64):

(qemu) system_wakeup
wake-up from suspend is not supported by this guest (qemu)

And this is the output of system_wakeup in a x86 guest that has the support but isn't suspended:

(qemu) system_wakeup
Unable to wake up: guest is not in suspended state (qemu)

Reported-by Balamuruhan S <[email protected]>

Signed-off-by Daniel Henrique Barboza <[email protected]>

---
 hmp.c                   | 5 ++++-
 hw/acpi/core.c          | 3 ++-
 hw/char/serial.c        | 2 +-
 hw/input/ps2.c          | 6 +++---
 hw/timer/mc146818rtc.c  | 2 +-
 include/sysemu/sysemu.h | 3 ++-
 migration/migration.c   | 4 ++--
 qapi/misc.json          | 8 +++++++-
 qmp.c                   | 8 +++++++-
 vl.c                    | 6 ++++--
 10 files changed, 33 insertions(+), 14 deletions(-)

hmp.c +4 -1

index 7828f93a39..0f5d943413 100644
@@ -1220,7 +1220,10 @@ void hmp_cont(Monitor *mon, const QDict *qdict)
 
 void hmp_system_wakeup(Monitor *mon, const QDict *qdict)
 {
-    qmp_system_wakeup(NULL);
+    Error *err = NULL;
+
+    qmp_system_wakeup(&err);
+    hmp_handle_error(mon, &err);
 }
 
 void hmp_nmi(Monitor *mon, const QDict *qdict)

hw/acpi/core.c +2 -1

index 52e18d7810..d6f0709691 100644
@@ -514,7 +514,8 @@ static uint32_t acpi_pm_tmr_get(ACPIREGS *ar)
 static void acpi_pm_tmr_timer(void *opaque)
 {
     ACPIREGS *ar = opaque;
-    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_PMTIMER);
+
+    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_PMTIMER, NULL);
     ar->tmr.update_sci(ar);
 }
 

hw/char/serial.c +1 -1

index 02463e3388..7c42a2abfc 100644
@@ -611,7 +611,7 @@ static void serial_receive1(void *opaque, const uint8_t *buf, int size)
     SerialState *s = opaque;
 
     if (s->wakeup) {
-        qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
+        qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
     }
     if(s->fcr & UART_FCR_FE) {
         int i;

hw/input/ps2.c +3 -3

index eb33ee9b6f..d3161f1e7c 100644
@@ -255,7 +255,7 @@ static void ps2_put_keycode(void *opaque, int keycode)
     PS2KbdState *s = opaque;
 
     trace_ps2_put_keycode(opaque, keycode);
-    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
+    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
 
     if (s->translate) {
         if (keycode == 0xf0) {

@@ -285,7 +285,7 @@ static void ps2_keyboard_event(DeviceState *dev, QemuConsole *src,
         return;
     }
 
-    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
+    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
     assert(evt->type == INPUT_EVENT_KIND_KEY);
     qcode = qemu_input_key_value_to_qcode(key->key);
 

@@ -748,7 +748,7 @@ static void ps2_mouse_sync(DeviceState *dev)
     }
 
     if (s->mouse_buttons) {
-        qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
+        qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
     }
     if (!(s->mouse_status & MOUSE_STATUS_REMOTE)) {
         /* if not remote, send event. Multiple events are sent if

hw/timer/mc146818rtc.c +1 -1

index e4e4de8b8a..69483152c3 100644
@@ -455,7 +455,7 @@ static void rtc_update_timer(void *opaque)
     if (qemu_clock_get_ns(rtc_clock) >= s->next_alarm_time) {
         irqs |= REG_C_AF;
         if (s->cmos_data[RTC_REG_B] & REG_B_AIE) {
-            qemu_system_wakeup_request(QEMU_WAKEUP_REASON_RTC);
+            qemu_system_wakeup_request(QEMU_WAKEUP_REASON_RTC, NULL);
         }
     }
 

include/sysemu/sysemu.h +2 -1

index 0446adacc6..162c4b16d9 100644
@@ -74,7 +74,8 @@ void qemu_exit_preconfig_request(void);
 void qemu_system_reset_request(ShutdownCause reason);
 void qemu_system_suspend_request(void);
 void qemu_register_suspend_notifier(Notifier *notifier);
-void qemu_system_wakeup_request(WakeupReason reason);
+bool qemu_wakeup_suspend_enabled(void);
+void qemu_system_wakeup_request(WakeupReason reason, Error **errp);
 void qemu_system_wakeup_enable(WakeupReason reason, bool enabled);
 void qemu_register_wakeup_notifier(Notifier *notifier);
 void qemu_register_wakeup_support(void);

migration/migration.c +2 -2

index 49ffb9997a..ffc4d9e556 100644
@@ -2408,7 +2408,7 @@ static int postcopy_start(MigrationState *ms)
     qemu_mutex_lock_iothread();
     trace_postcopy_start_set_run();
 
-    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
+    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
     global_state_store();
     ret = vm_stop_force_state(RUN_STATE_FINISH_MIGRATE);
     if (ret < 0) {

@@ -2612,7 +2612,7 @@ static void migration_completion(MigrationState *s)
     if (s->state == MIGRATION_STATUS_ACTIVE) {
         qemu_mutex_lock_iothread();
         s->downtime_start = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
-        qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
+        qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
         s->vm_was_running = runstate_is_running();
         ret = global_state_store();
 

qapi/misc.json +7 -1

index deb982ed38..03df2c37cf 100644
@@ -1235,12 +1235,18 @@
 ##
 # @system_wakeup:
 #
-# Wakeup guest from suspend.  Does nothing in case the guest isn't suspended.
+# Wake up guest from suspend. If the guest has wake-up from suspend
+# support enabled (wakeup-suspend-support flag from
+# query-current-machine), wake-up guest from suspend if the guest is
+# in SUSPENDED state. Return an error otherwise.
 #
 # Since:  1.1
 #
 # Returns:  nothing.
 #
+# Note: prior to 4.0, this command does nothing in case the guest
+# isn't suspended.
+#
 # Example:
 #
 # -> { "execute": "system_wakeup" }

qmp.c +7 -1

index e7c0a2fd60..f557d1617d 100644
@@ -183,7 +183,13 @@ void qmp_cont(Error **errp)
 
 void qmp_system_wakeup(Error **errp)
 {
-    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER);
+    if (!qemu_wakeup_suspend_enabled()) {
+        error_setg(errp,
+                   "wake-up from suspend is not supported by this guest");
+        return;
+    }
+
+    qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, errp);
 }
 
 ObjectPropertyInfoList *qmp_qom_list(const char *path, Error **errp)

vl.c +4 -2

index 8f5b3ef4e9..5b51bbc47c 100644
@@ -1752,11 +1752,13 @@ void qemu_register_suspend_notifier(Notifier *notifier)
     notifier_list_add(&suspend_notifiers, notifier);
 }
 
-void qemu_system_wakeup_request(WakeupReason reason)
+void qemu_system_wakeup_request(WakeupReason reason, Error **errp)
 {
     trace_system_wakeup_request(reason);
 
     if (!runstate_check(RUN_STATE_SUSPENDED)) {
+        error_setg(errp,
+                   "Unable to wake up: guest is not in suspended state");
         return;
     }
     if (!(wakeup_reason_mask & (1 << reason))) {

@@ -1786,7 +1788,7 @@ void qemu_register_wakeup_support(void)
     wakeup_suspend_enabled = true;
 }
 
-static bool qemu_wakeup_suspend_enabled(void)
+bool qemu_wakeup_suspend_enabled(void)
 {
     return wakeup_suspend_enabled;
 }

Signature · 1 line

2.19.2

Quoted 9 lines · Markus Armbruster

Quoted 6 lines · Daniel Henrique Barboza

changes in v11:
- fixed typos, changed version to 4.0 in patches 1 and 3
- changed text in patch 2 to be less alarming
- patch 3: changed error handling
- previous version link:
http://lists.nongnu.org/archive/html/qemu-devel/2018-11/msg01774.html

Quoted 1 line

Looks ready to me. Who's going to merge it?

Do you mind merging it through the QMP tree?

Acked-by Eduardo Habkost <[email protected]>