[PULL 12/12] mc146818rtc: fix timer interrupt reinjection again

[Paolo Bonzini <pbonzini@redhat.com>]

Commit 369b41359af46bded5799c9ef8be2b641d92e043 broke timer interrupt
reinjection when there is no period change by the guest.  In that
case, old_period is 0, which ends up zeroing irq_coalesced (counter of
reinjected interrupts).

The consequence is Windows 7 is unable to synchronize time via NTP.
Easily reproducible by playing a fullscreen video with cirrus and VNC.

Fix by passing s->period when periodic_timer_update is called due to
expiration of the timer.  With this change, old_period == 0 only
means that the periodic timer was off.

Reported-by: Marcelo Tosatti <mtosatti@redhat.com>
Co-developed-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/rtc/mc146818rtc.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/hw/rtc/mc146818rtc.c b/hw/rtc/mc146818rtc.c
index 9869dc5..74ae74b 100644
--- a/hw/rtc/mc146818rtc.c
+++ b/hw/rtc/mc146818rtc.c
@@ -168,12 +168,14 @@ static uint32_t rtc_periodic_clock_ticks(RTCState *s)
  * is just due to period adjustment.
  */
 static void
-periodic_timer_update(RTCState *s, int64_t current_time, uint32_t old_period)
+periodic_timer_update(RTCState *s, int64_t current_time, uint32_t old_period, bool period_change)
 {
     uint32_t period;
     int64_t cur_clock, next_irq_clock, lost_clock = 0;
 
     period = rtc_periodic_clock_ticks(s);
+    s->period = period;
+
     if (!period) {
         s->irq_coalesced = 0;
         timer_del(s->periodic_timer);
@@ -188,7 +190,7 @@ periodic_timer_update(RTCState *s, int64_t current_time, uint32_t old_period)
      * if the periodic timer's update is due to period re-configuration,
      * we should count the clock since last interrupt.
      */
-    if (old_period) {
+    if (old_period && period_change) {
         int64_t last_periodic_clock, next_periodic_clock;
 
         next_periodic_clock = muldiv64(s->next_periodic_time,
@@ -215,7 +217,6 @@ periodic_timer_update(RTCState *s, int64_t current_time, uint32_t old_period)
     if (s->lost_tick_policy == LOST_TICK_POLICY_SLEW) {
         uint32_t old_irq_coalesced = s->irq_coalesced;
 
-        s->period = period;
         lost_clock += old_irq_coalesced * old_period;
         s->irq_coalesced = lost_clock / s->period;
         lost_clock %= s->period;
@@ -245,7 +246,7 @@ static void rtc_periodic_timer(void *opaque)
 {
     RTCState *s = opaque;
 
-    periodic_timer_update(s, s->next_periodic_time, 0);
+    periodic_timer_update(s, s->next_periodic_time, s->period, false);
     s->cmos_data[RTC_REG_C] |= REG_C_PF;
     if (s->cmos_data[RTC_REG_B] & REG_B_PIE) {
         s->cmos_data[RTC_REG_C] |= REG_C_IRQF;
@@ -511,7 +512,7 @@ static void cmos_ioport_write(void *opaque, hwaddr addr,
 
             if (update_periodic_timer) {
                 periodic_timer_update(s, qemu_clock_get_ns(rtc_clock),
-                                      old_period);
+                                      old_period, true);
             }
 
             check_update_timer(s);
@@ -550,7 +551,7 @@ static void cmos_ioport_write(void *opaque, hwaddr addr,
 
             if (update_periodic_timer) {
                 periodic_timer_update(s, qemu_clock_get_ns(rtc_clock),
-                                      old_period);
+                                      old_period, true);
             }
 
             check_update_timer(s);
@@ -794,6 +795,7 @@ static int rtc_post_load(void *opaque, int version_id)
         s->offset = 0;
         check_update_timer(s);
     }
+    s->period = rtc_periodic_clock_ticks(s);
 
     /* The periodic timer is deterministic in record/replay mode,
      * so there is no need to update it after loading the vmstate.
@@ -803,7 +805,7 @@ static int rtc_post_load(void *opaque, int version_id)
         uint64_t now = qemu_clock_get_ns(rtc_clock);
         if (now < s->next_periodic_time ||
             now > (s->next_periodic_time + get_max_clock_jump())) {
-            periodic_timer_update(s, qemu_clock_get_ns(rtc_clock), 0);
+            periodic_timer_update(s, qemu_clock_get_ns(rtc_clock), s->period, false);
         }
     }
 
-- 
1.8.3.1