[Xen-devel] [PATCH RFC 2/3] x86/hvm/rtc: Inject RTC periodic interupts from the vpt code.

[Tim Deegan <tim@xxxxxxx>]

Let the vpt code drive the RTC's timer interrupts directly, as it does
for other periodic time sources, and fix up the register state in a
vpt callback when the interrupt is injected.

This fixes a hang seen on Windows 2003 in no-missed-ticks mode, where
when a tick was pending, the early callback from the VPT code would
always set REG_C.PF on every VMENTER; meanwhile the guest was in its
interrupt handler reading REG_C in a loop and waiting to see it clear.

One drawback is that a guest that attempts to suppress RTC periodic
interrupts by failing to read REG_C will receive up to 10 spurious
interrupts, even in 'strict' mode.  However:
 - since all previous RTC models have had this property (including
   the current one, since 'no-ack' mode is hard-coded on) we're
   pretty sure that all guests can handle this; and
 - we're already playing some other interesting games with this
   interrupt in the vpt code.

One other corner case: a guest that enables the PF timer interrupt,
masks the interupt in the APIC and then polls REG_C looking for PF
will not see PF getting set.  The more likely case of enabling the
timers and masking the interrupt with REG_B.PIE is already handled
correctly.

Signed-off-by: Tim Deegan <tim@xxxxxxx>
---
 xen/arch/x86/hvm/rtc.c        | 25 +++++++++++--------------
 xen/arch/x86/hvm/vpt.c        | 40 ----------------------------------------
 xen/include/asm-x86/hvm/vpt.h |  1 -
 3 files changed, 11 insertions(+), 55 deletions(-)

diff --git a/xen/arch/x86/hvm/rtc.c b/xen/arch/x86/hvm/rtc.c
index cfc1af9..18a4fe8 100644
--- a/xen/arch/x86/hvm/rtc.c
+++ b/xen/arch/x86/hvm/rtc.c
@@ -78,29 +78,26 @@ static void rtc_update_irq(RTCState *s)
     hvm_isa_irq_assert(vrtc_domain(s), RTC_IRQ);
 }
 
-bool_t rtc_periodic_interrupt(void *opaque)
+/* Called by the VPT code after it's injected a PF interrupt for us.
+ * Fix up the register state to reflect what happened. */
+static void rtc_pf_callback(struct vcpu *v, void *opaque)
 {
     RTCState *s = opaque;
-    bool_t ret;
 
     spin_lock(&s->lock);
-    ret = rtc_mode_is(s, no_ack) || !(s->hw.cmos_data[RTC_REG_C] & RTC_IRQF);
-    if ( rtc_mode_is(s, no_ack) || !(s->hw.cmos_data[RTC_REG_C] & RTC_PF) )
-    {
-        s->hw.cmos_data[RTC_REG_C] |= RTC_PF;
-        rtc_update_irq(s);
-    }
-    else if ( ++(s->pt_dead_ticks) >= 10 )
+
+    if ( !rtc_mode_is(s, no_ack)
+         && (s->hw.cmos_data[RTC_REG_C] & RTC_IRQF)
+         && ++(s->pt_dead_ticks) >= 10 )
     {
         /* VM is ignoring its RTC; no point in running the timer */
         destroy_periodic_time(&s->pt);
         s->period = 0;
     }
-    if ( !(s->hw.cmos_data[RTC_REG_C] & RTC_IRQF) )
-        ret = 0;
-    spin_unlock(&s->lock);
 
-    return ret;
+    s->hw.cmos_data[RTC_REG_C] |= RTC_PF|RTC_IRQF;
+
+    spin_unlock(&s->lock);
 }
 
 /* Check whether the REG_C.PF bit should have been set by a tick since
@@ -156,7 +153,7 @@ static void rtc_timer_update(RTCState *s)
                     delta = period - ((now - s->start_time) % period);
                 if ( s->hw.cmos_data[RTC_REG_B] & RTC_PIE )
                     create_periodic_time(v, &s->pt, delta, period,
-                                         RTC_IRQ, NULL, s);
+                                         RTC_IRQ, rtc_pf_callback, s);
                 else
                     s->check_ticks_since = now;
             }
diff --git a/xen/arch/x86/hvm/vpt.c b/xen/arch/x86/hvm/vpt.c
index 1961bda..f7af688 100644
--- a/xen/arch/x86/hvm/vpt.c
+++ b/xen/arch/x86/hvm/vpt.c
@@ -231,12 +231,9 @@ int pt_update_irq(struct vcpu *v)
     struct periodic_time *pt, *temp, *earliest_pt;
     uint64_t max_lag;
     int irq, is_lapic;
-    void *pt_priv;
 
- rescan:
     spin_lock(&v->arch.hvm_vcpu.tm_lock);
 
- rescan_locked:
     earliest_pt = NULL;
     max_lag = -1ULL;
     list_for_each_entry_safe ( pt, temp, head, list )
@@ -270,48 +267,11 @@ 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 )
-    {
-        if ( !rtc_periodic_interrupt(pt_priv) )
-            irq = -1;
-
-        pt_lock(earliest_pt);
-
-        if ( irq < 0 && earliest_pt->pending_intr_nr )
-        {
-            /*
-             * RTC periodic timer runs without the corresponding interrupt
-             * being enabled - need to mimic enough of pt_intr_post() to keep
-             * things going.
-             */
-            earliest_pt->pending_intr_nr = 0;
-            earliest_pt->irq_issued = 0;
-            set_timer(&earliest_pt->timer, earliest_pt->scheduled);
-        }
-        else if ( irq >= 0 && pt_irq_masked(earliest_pt) )
-        {
-            if ( earliest_pt->on_list )
-            {
-                /* suspend timer emulation */
-                list_del(&earliest_pt->list);
-                earliest_pt->on_list = 0;
-            }
-            irq = -1;
-        }
-
-        /* Avoid dropping the lock if we can. */
-        if ( irq < 0 && v == earliest_pt->vcpu )
-            goto rescan_locked;
-        pt_unlock(earliest_pt);
-        if ( irq < 0 )
-            goto rescan;
-    }
     else
     {
         hvm_isa_irq_deassert(v->domain, irq);
diff --git a/xen/include/asm-x86/hvm/vpt.h b/xen/include/asm-x86/hvm/vpt.h
index 9f48635..7d62653 100644
--- a/xen/include/asm-x86/hvm/vpt.h
+++ b/xen/include/asm-x86/hvm/vpt.h
@@ -184,7 +184,6 @@ 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);
-bool_t rtc_periodic_interrupt(void *);
 
 void pmtimer_init(struct vcpu *v);
 void pmtimer_deinit(struct domain *d);
-- 
1.8.5.2


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