x86 hvm: suspend platform timer emulation while its IRQ is masked

This patch gets rid of a timer which IRQ is masked from vcpu's timer
list. It reduces the overhead of VM EXIT and context switch of vm.

Also fixes a potential bug.
(1) VCPU#0: mask the IRQ of a timer. (ex. vioapic.redir[2].mask=1)
(2) VCPU#1: pt_timer_fn() is invoked by expiration of the timer.
(3) VCPU#1: pt_update_irq() is called but does nothing by
pt_irq_masked()==1.
(4) VCPU#1: sleep by halt.
(5) VCPU#0: unmask the IRQ of the timer.
After that, no one wakes up the VCPU#1.

IRQ of ISA is masked by:
 - PIC's IMR
 - IOAPIC's redir[0]
 - IOAPIC's redir[N].mask
 - LAPIC's LVT0
 - LAPIC enabled/disabled

IRQ of LAPIC timer is masked by:
 - LAPIC's LVTT
 - LAPIC disabled

When above stuffs are changed, the corresponding vcpu is kicked and
suspended timer emulation is resumed.

In addition, a small bug fix in pt_adjust_global_vcpu_target().

Signed-off-by: Kouya Shimura <kouya@jp.fujitsu.com>

1 files changed, 53 insertions, 7 deletions

diff --git a/xen/arch/x86/hvm/vpt.c b/xen/arch/x86/hvm/vpt.c
index f586d242d1..1a5804a356 100644
--- a/xen/arch/x86/hvm/vpt.c
+++ b/xen/arch/x86/hvm/vpt.c
@@ -216,19 +216,30 @@ static void pt_timer_fn(void *data)
 void pt_update_irq(struct vcpu *v)
 {
     struct list_head *head = &v->arch.hvm_vcpu.tm_list;
-    struct periodic_time *pt, *earliest_pt = NULL;
+    struct periodic_time *pt, *temp, *earliest_pt = NULL;
     uint64_t max_lag = -1ULL;
     int irq, is_lapic;
 
     spin_lock(&v->arch.hvm_vcpu.tm_lock);
 
-    list_for_each_entry ( pt, head, list )
+    list_for_each_entry_safe ( pt, temp, head, list )
     {
-        if ( pt->pending_intr_nr && !pt_irq_masked(pt) &&
-             ((pt->last_plt_gtime + pt->period) < max_lag) )
+        if ( pt->pending_intr_nr )
         {
-            max_lag = pt->last_plt_gtime + pt->period;
-            earliest_pt = pt;
+            if ( pt_irq_masked(pt) )
+            {
+                /* suspend timer emulation */
+                list_del(&pt->list);
+                pt->on_list = 0;
+            }
+            else
+            {
+                if ( (pt->last_plt_gtime + pt->period) < max_lag )
+                {
+                    max_lag = pt->last_plt_gtime + pt->period;
+                    earliest_pt = pt;
+                }
+            }
         }
     }
 
@@ -412,6 +423,7 @@ void destroy_periodic_time(struct periodic_time *pt)
     if ( pt->on_list )
         list_del(&pt->list);
     pt->on_list = 0;
+    pt->pending_intr_nr = 0;
     pt_unlock(pt);
 
     /*
@@ -451,12 +463,14 @@ static void pt_adjust_vcpu(struct periodic_time *pt, struct vcpu *v)
 
 void pt_adjust_global_vcpu_target(struct vcpu *v)
 {
-    struct pl_time *pl_time = &v->domain->arch.hvm_domain.pl_time;
+    struct pl_time *pl_time;
     int i;
 
     if ( v == NULL )
         return;
 
+    pl_time = &v->domain->arch.hvm_domain.pl_time;
+
     spin_lock(&pl_time->vpit.lock);
     pt_adjust_vcpu(&pl_time->vpit.pt0, v);
     spin_unlock(&pl_time->vpit.lock);
@@ -470,3 +484,35 @@ void pt_adjust_global_vcpu_target(struct vcpu *v)
         pt_adjust_vcpu(&pl_time->vhpet.pt[i], v);
     spin_unlock(&pl_time->vhpet.lock);
 }
+
+
+static void pt_resume(struct periodic_time *pt)
+{
+    if ( pt->vcpu == NULL )
+        return;
+
+    pt_lock(pt);
+    if ( pt->pending_intr_nr && !pt->on_list )
+    {
+        pt->on_list = 1;
+        list_add(&pt->list, &pt->vcpu->arch.hvm_vcpu.tm_list);
+        vcpu_kick(pt->vcpu);
+    }
+    pt_unlock(pt);
+}
+
+void pt_may_unmask_irq(struct domain *d, struct periodic_time *vlapic_pt)
+{
+    int i;
+
+    if ( d )
+    {
+        pt_resume(&d->arch.hvm_domain.pl_time.vpit.pt0);
+        pt_resume(&d->arch.hvm_domain.pl_time.vrtc.pt);
+        for ( i = 0; i < HPET_TIMER_NUM; i++ )
+            pt_resume(&d->arch.hvm_domain.pl_time.vhpet.pt[i]);
+    }
+
+    if ( vlapic_pt )
+        pt_resume(vlapic_pt);
+}