KVM: PIT: fix injection logic and count

The PIT injection logic is problematic under the following cases:

1) If there is a higher priority vector to be delivered by the time
kvm_pit_timer_intr_post is invoked ps->inject_pending won't be set.
This opens the possibility for missing many PIT event injections (say if
guest executes hlt at this point).

2) ps->inject_pending is racy with more than two vcpus. Since there's no locking
around read/dec of pt->pending, two vcpu's can inject two interrupts for a single
pt->pending count.

Fix 1 by using an irq ack notifier: only reinject when the previous irq
has been acked. Fix 2 with appropriate locking around manipulation of
pending count and irq_ack by the injection / ack paths.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index c0f7872..7d04dd3 100644 (file)
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -207,6 +207,8 @@ static int __pit_timer_fn(struct kvm_kpit_state *ps)
 
        pt->timer.expires = ktime_add_ns(pt->timer.expires, pt->period);
        pt->scheduled = ktime_to_ns(pt->timer.expires);
+       if (pt->period)
+               ps->channels[0].count_load_time = pt->timer.expires;
 
        return (pt->period == 0 ? 0 : 1);
 }
@@ -215,12 +217,22 @@ int pit_has_pending_timer(struct kvm_vcpu *vcpu)
 {
        struct kvm_pit *pit = vcpu->kvm->arch.vpit;
 
-       if (pit && vcpu->vcpu_id == 0 && pit->pit_state.inject_pending)
+       if (pit && vcpu->vcpu_id == 0 && pit->pit_state.irq_ack)
                return atomic_read(&pit->pit_state.pit_timer.pending);
-
        return 0;
 }
 
+void kvm_pit_ack_irq(struct kvm_irq_ack_notifier *kian)
+{
+       struct kvm_kpit_state *ps = container_of(kian, struct kvm_kpit_state,
+                                                irq_ack_notifier);
+       spin_lock(&ps->inject_lock);
+       if (atomic_dec_return(&ps->pit_timer.pending) < 0)
+               WARN_ON(1);
+       ps->irq_ack = 1;
+       spin_unlock(&ps->inject_lock);
+}
+
 static enum hrtimer_restart pit_timer_fn(struct hrtimer *data)
 {
        struct kvm_kpit_state *ps;
@@ -255,8 +267,9 @@ static void destroy_pit_timer(struct kvm_kpit_timer *pt)
        hrtimer_cancel(&pt->timer);
 }
 
-static void create_pit_timer(struct kvm_kpit_timer *pt, u32 val, int is_period)
+static void create_pit_timer(struct kvm_kpit_state *ps, u32 val, int is_period)
 {
+       struct kvm_kpit_timer *pt = &ps->pit_timer;
        s64 interval;
 
        interval = muldiv64(val, NSEC_PER_SEC, KVM_PIT_FREQ);
@@ -268,6 +281,7 @@ static void create_pit_timer(struct kvm_kpit_timer *pt, u32 val, int is_period)
        pt->period = (is_period == 0) ? 0 : interval;
        pt->timer.function = pit_timer_fn;
        atomic_set(&pt->pending, 0);
+       ps->irq_ack = 1;
 
        hrtimer_start(&pt->timer, ktime_add_ns(ktime_get(), interval),
                      HRTIMER_MODE_ABS);
@@ -302,11 +316,11 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
        case 1:
         /* FIXME: enhance mode 4 precision */
        case 4:
-               create_pit_timer(&ps->pit_timer, val, 0);
+               create_pit_timer(ps, val, 0);
                break;
        case 2:
        case 3:
-               create_pit_timer(&ps->pit_timer, val, 1);
+               create_pit_timer(ps, val, 1);
                break;
        default:
                destroy_pit_timer(&ps->pit_timer);
@@ -520,7 +534,7 @@ void kvm_pit_reset(struct kvm_pit *pit)
        mutex_unlock(&pit->pit_state.lock);
 
        atomic_set(&pit->pit_state.pit_timer.pending, 0);
-       pit->pit_state.inject_pending = 1;
+       pit->pit_state.irq_ack = 1;
 }
 
 struct kvm_pit *kvm_create_pit(struct kvm *kvm)
@@ -534,6 +548,7 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm)
 
        mutex_init(&pit->pit_state.lock);
        mutex_lock(&pit->pit_state.lock);
+       spin_lock_init(&pit->pit_state.inject_lock);
 
        /* Initialize PIO device */
        pit->dev.read = pit_ioport_read;
@@ -555,6 +570,9 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm)
        pit_state->pit = pit;
        hrtimer_init(&pit_state->pit_timer.timer,
                     CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+       pit_state->irq_ack_notifier.gsi = 0;
+       pit_state->irq_ack_notifier.irq_acked = kvm_pit_ack_irq;
+       kvm_register_irq_ack_notifier(kvm, &pit_state->irq_ack_notifier);
        mutex_unlock(&pit->pit_state.lock);
 
        kvm_pit_reset(pit);
@@ -592,37 +610,19 @@ void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu)
        struct kvm_kpit_state *ps;
 
        if (vcpu && pit) {
+               int inject = 0;
                ps = &pit->pit_state;
 
-               /* Try to inject pending interrupts when:
-                * 1. Pending exists
-                * 2. Last interrupt was accepted or waited for too long time*/
-               if (atomic_read(&ps->pit_timer.pending) &&
-                   (ps->inject_pending ||
-                   (jiffies - ps->last_injected_time
-                               >= KVM_MAX_PIT_INTR_INTERVAL))) {
-                       ps->inject_pending = 0;
-                       __inject_pit_timer_intr(kvm);
-                       ps->last_injected_time = jiffies;
-               }
-       }
-}
-
-void kvm_pit_timer_intr_post(struct kvm_vcpu *vcpu, int vec)
-{
-       struct kvm_arch *arch = &vcpu->kvm->arch;
-       struct kvm_kpit_state *ps;
-
-       if (vcpu && arch->vpit) {
-               ps = &arch->vpit->pit_state;
-               if (atomic_read(&ps->pit_timer.pending) &&
-               (((arch->vpic->pics[0].imr & 1) == 0 &&
-                 arch->vpic->pics[0].irq_base == vec) ||
-                 (arch->vioapic->redirtbl[0].fields.vector == vec &&
-                 arch->vioapic->redirtbl[0].fields.mask != 1))) {
-                       ps->inject_pending = 1;
-                       atomic_dec(&ps->pit_timer.pending);
-                       ps->channels[0].count_load_time = ktime_get();
+               /* Try to inject pending interrupts when
+                * last one has been acked.
+                */
+               spin_lock(&ps->inject_lock);
+               if (atomic_read(&ps->pit_timer.pending) && ps->irq_ack) {
+                       ps->irq_ack = 0;
+                       inject = 1;
                }
+               spin_unlock(&ps->inject_lock);
+               if (inject)
+                       __inject_pit_timer_intr(kvm);
        }
 }

diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
index db25c2a..e436d49 100644 (file)
--- a/arch/x86/kvm/i8254.h
+++ b/arch/x86/kvm/i8254.h
@@ -8,7 +8,6 @@ struct kvm_kpit_timer {
        int irq;
        s64 period; /* unit: ns */
        s64 scheduled;
-       ktime_t last_update;
        atomic_t pending;
 };
 
@@ -34,8 +33,9 @@ struct kvm_kpit_state {
        u32    speaker_data_on;
        struct mutex lock;
        struct kvm_pit *pit;
-       bool inject_pending; /* if inject pending interrupts */
-       unsigned long last_injected_time;
+       spinlock_t inject_lock;
+       unsigned long irq_ack;
+       struct kvm_irq_ack_notifier irq_ack_notifier;
 };
 
 struct kvm_pit {
@@ -54,7 +54,6 @@ struct kvm_pit {
 #define KVM_PIT_CHANNEL_MASK       0x3
 
 void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu);
-void kvm_pit_timer_intr_post(struct kvm_vcpu *vcpu, int vec);
 void kvm_pit_load_count(struct kvm *kvm, int channel, u32 val);
 struct kvm_pit *kvm_create_pit(struct kvm *kvm);
 void kvm_free_pit(struct kvm *kvm);

diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index 3c508af..8c1b9c5 100644 (file)
--- a/arch/x86/kvm/irq.c
+++ b/arch/x86/kvm/irq.c
@@ -90,7 +90,6 @@ EXPORT_SYMBOL_GPL(kvm_inject_pending_timer_irqs);
 void kvm_timer_intr_post(struct kvm_vcpu *vcpu, int vec)
 {
        kvm_apic_timer_intr_post(vcpu, vec);
-       kvm_pit_timer_intr_post(vcpu, vec);
        /* TODO: PIT, RTC etc. */
 }
 EXPORT_SYMBOL_GPL(kvm_timer_intr_post);