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Subject[PATCH 32/40] KVM: PIT: fix injection logic and count
Date
From: Marcelo Tosatti <mtosatti@redhat.com>

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>
---
arch/x86/kvm/i8254.c | 70 +++++++++++++++++++++++++-------------------------
arch/x86/kvm/i8254.h | 7 ++---
arch/x86/kvm/irq.c | 1 -
3 files changed, 38 insertions(+), 40 deletions(-)
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index c0f7872..7d04dd3 100644
--- 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
--- 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
--- 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);
--
1.6.0.1


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