x86/HVM: assorted RTC emulation adjustments

- only call check_update_timer() on REG_B writes when SET changes
- only call alarm_timer_update() on REG_B writes when relevant bits
  change
- instead properly handle AF and PF when the guest is not also setting
  AIE/PIE respectively (for UF this was already the case, only a
  comment was slightly inaccurate), including calling the respective
  update functions upon REG_C reads

--- a/xen/arch/x86/hvm/rtc.c
+++ b/xen/arch/x86/hvm/rtc.c
@@ -60,12 +60,19 @@ static void rtc_toggle_irq(RTCState *s)
     hvm_isa_irq_assert(d, RTC_IRQ);
 }
 
-static void rtc_periodic_cb(struct vcpu *v, void *opaque)
+void rtc_periodic_interrupt(void *opaque)
 {
     RTCState *s = opaque;
 
     spin_lock(&s->lock);
-    s->hw.cmos_data[RTC_REG_C] |= RTC_PF | RTC_IRQF;
+    if ( s->hw.cmos_data[RTC_REG_C] & RTC_PF )
+        destroy_periodic_time(&s->pt);
+    else
+    {
+        s->hw.cmos_data[RTC_REG_C] |= RTC_PF;
+        if ( s->hw.cmos_data[RTC_REG_B] & RTC_PIE )
+            rtc_toggle_irq(s);
+    }
     spin_unlock(&s->lock);
 }
 
@@ -91,8 +98,7 @@ static void rtc_timer_update(RTCState *s
         {
             period = 1 << (period_code - 1); /* period in 32 Khz cycles */
             period = DIV_ROUND(period * 1000000000ULL, 32768); /* in ns */
-            create_periodic_time(v, &s->pt, period, period, RTC_IRQ,
-                                 rtc_periodic_cb, s);
+            create_periodic_time(v, &s->pt, period, period, RTC_IRQ, NULL, s);
             break;
         }
         /* fall through */
@@ -120,7 +126,7 @@ static void check_update_timer(RTCState 
         guest_usec = get_localtime_us(d) % USEC_PER_SEC;
         if (guest_usec >= (USEC_PER_SEC - 244))
         {
-            /* RTC is in update cycle when enabling UIE */
+            /* RTC is in update cycle */
             s->hw.cmos_data[RTC_REG_A] |= RTC_UIP;
             next_update_time = (USEC_PER_SEC - guest_usec) * NS_PER_USEC;
             expire_time = NOW() + next_update_time;
@@ -188,7 +194,7 @@ static void alarm_timer_update(RTCState 
 
     stop_timer(&s->alarm_timer);
 
-    if ((s->hw.cmos_data[RTC_REG_B] & RTC_AIE) &&
+    if (!(s->hw.cmos_data[RTC_REG_C] & RTC_AF) &&
             !(s->hw.cmos_data[RTC_REG_B] & RTC_SET))
     {
         s->current_tm = gmtime(get_localtime(d));
@@ -455,8 +461,10 @@ static int rtc_ioport_write(void *opaque
                 break;
             }
         s->hw.cmos_data[RTC_REG_B] = data;
-        check_update_timer(s);
-        alarm_timer_update(s);
+        if ( (data ^ orig) & RTC_SET )
+            check_update_timer(s);
+        if ( (data ^ orig) & (RTC_24H | RTC_DM_BINARY | RTC_SET) )
+            alarm_timer_update(s);
         break;
     case RTC_REG_C:
     case RTC_REG_D:
@@ -610,6 +618,8 @@ static uint32_t rtc_ioport_read(RTCState
         hvm_isa_irq_deassert(vrtc_domain(s), RTC_IRQ);
         s->hw.cmos_data[RTC_REG_C] = 0x00;
         check_update_timer(s);
+        alarm_timer_update(s);
+        rtc_timer_update(s);
         break;
     default:
         ret = s->hw.cmos_data[s->hw.cmos_index];
--- a/xen/arch/x86/hvm/vpt.c
+++ b/xen/arch/x86/hvm/vpt.c
@@ -22,6 +22,7 @@
 #include <asm/hvm/vpt.h>
 #include <asm/event.h>
 #include <asm/apic.h>
+#include <asm/mc146818rtc.h>
 
 #define mode_is(d, name) \
     ((d)->arch.hvm_domain.params[HVM_PARAM_TIMER_MODE] == HVMPTM_##name)
@@ -218,6 +219,7 @@ int pt_update_irq(struct vcpu *v)
     struct periodic_time *pt, *temp, *earliest_pt = NULL;
     uint64_t max_lag = -1ULL;
     int irq, is_lapic;
+    void *pt_priv;
 
     spin_lock(&v->arch.hvm_vcpu.tm_lock);
 
@@ -251,13 +253,14 @@ int pt_update_irq(struct vcpu *v)
     earliest_pt->irq_issued = 1;
     irq = earliest_pt->irq;
     is_lapic = (earliest_pt->source == PTSRC_lapic);
+    pt_priv = earliest_pt->priv;
 
     spin_unlock(&v->arch.hvm_vcpu.tm_lock);
 
     if ( is_lapic )
-    {
         vlapic_set_irq(vcpu_vlapic(v), irq, 0);
-    }
+    else if ( irq == RTC_IRQ && pt_priv )
+        rtc_periodic_interrupt(pt_priv);
     else
     {
         hvm_isa_irq_deassert(v->domain, irq);
--- a/xen/include/asm-x86/hvm/vpt.h
+++ b/xen/include/asm-x86/hvm/vpt.h
@@ -181,6 +181,7 @@ void rtc_migrate_timers(struct vcpu *v);
 void rtc_deinit(struct domain *d);
 void rtc_reset(struct domain *d);
 void rtc_update_clock(struct domain *d);
+void rtc_periodic_interrupt(void *);
 
 void pmtimer_init(struct vcpu *v);
 void pmtimer_deinit(struct domain *d);