mc146818rtc: add rtc-reset-reinjection QMP command

It is necessary to reset RTC interrupt reinjection backlog if
guest time is synchronized via a different mechanism, such as
QGA's guest-set-time command.

Failing to do so causes both corrections to be applied (summed),
resulting in an incorrect guest time.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/timer/mc146818rtc.c

@@ -27,6 +27,7 @@
 #include "hw/timer/mc146818rtc.h"
 #include "qapi/visitor.h"
 #include "qapi-event.h"
+#include "qmp-commands.h"
 
 #ifdef TARGET_I386
 #include "hw/i386/apic.h"
@@ -85,6 +86,7 @@ typedef struct RTCState {
     Notifier clock_reset_notifier;
     LostTickPolicy lost_tick_policy;
     Notifier suspend_notifier;
+    QLIST_ENTRY(RTCState) link;
 } RTCState;
 
 static void rtc_set_time(RTCState *s);
@@ -523,6 +525,20 @@ static void rtc_get_time(RTCState *s, struct tm *tm)
         rtc_from_bcd(s, s->cmos_data[RTC_CENTURY]) * 100 - 1900;
 }
 
+static QLIST_HEAD(, RTCState) rtc_devices =
+    QLIST_HEAD_INITIALIZER(rtc_devices);
+
+#ifdef TARGET_I386
+void qmp_rtc_reset_reinjection(Error **errp)
+{
+    RTCState *s;
+
+    QLIST_FOREACH(s, &rtc_devices, link) {
+        s->irq_coalesced = 0;
+    }
+}
+#endif
+
 static void rtc_set_time(RTCState *s)
 {
     struct tm tm;
@@ -911,6 +927,8 @@ ISADevice *rtc_init(ISABus *bus, int base_year, qemu_irq intercept_irq)
     } else {
         isa_init_irq(isadev, &s->irq, RTC_ISA_IRQ);
     }
+    QLIST_INSERT_HEAD(&rtc_devices, s, link);
+
     return isadev;
 }
 

monitor.c

@@ -5441,3 +5441,10 @@ QemuOptsList qemu_mon_opts = {
         { /* end of list */ }
     },
 };
+
+#ifndef TARGET_I386
+void qmp_rtc_reset_reinjection(Error **errp)
+{
+    error_set(errp, QERR_FEATURE_DISABLED, "rtc-reset-reinjection");
+}
+#endif

qapi-schema.json

@@ -3468,3 +3468,15 @@
 ##
 { 'enum': 'GuestPanicAction',
   'data': [ 'pause' ] }
+
+##
+# @rtc-reset-reinjection
+#
+# This command will reset the RTC interrupt reinjection backlog.
+# Can be used if another mechanism to synchronize guest time
+# is in effect, for example QEMU guest agent's guest-set-time
+# command.
+#
+# Since: 2.1
+##
+{ 'command': 'rtc-reset-reinjection' }

qmp-commands.hx

@@ -3675,3 +3675,26 @@ Example:
                  { "slot": "3", "slot-type": "DIMM", "source": 0, "status": 0}
    ]}
 EQMP
+
+#if defined TARGET_I386
+    {
+        .name       = "rtc-reset-reinjection",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_input_rtc_reset_reinjection,
+    },
+#endif
+
+SQMP
+rtc-reset-reinjection
+---------------------
+
+Reset the RTC interrupt reinjection backlog.
+
+Arguments: None.
+
+Example:
+
+-> { "execute": "rtc-reset-reinjection" }
+<- { "return": {} }
+
+EQMP