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>

1 files changed, 3 insertions, 4 deletions

diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
index db25c2a6c8c4..e436d4983aa1 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);