KVM: x86: Introduce a workqueue to deliver PIT timer interrupts

We really want to "kvm_set_irq" during the hrtimer callback,
but that is risky because that is during interrupt context.
Instead, offload the work to a workqueue, which is a bit safer
and should provide most of the same functionality.

Signed-off-by: Chris Lalancette <clalance@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 188d82762c1bbcbaba59d33c0d87857adf536dba..467cc47fb7334bfd485ea627f2315b1e7aa9eeb3 100644 (file)
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -34,6 +34,7 @@
 
 #include <linux/kvm_host.h>
 #include <linux/slab.h>
+#include <linux/workqueue.h>
 
 #include "irq.h"
 #include "i8254.h"
@@ -244,11 +245,22 @@ static 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);
-       raw_spin_lock(&ps->inject_lock);
-       if (atomic_dec_return(&ps->pit_timer.pending) < 0)
+       int value;
+
+       spin_lock(&ps->inject_lock);
+       value = atomic_dec_return(&ps->pit_timer.pending);
+       if (value < 0)
+               /* spurious acks can be generated if, for example, the
+                * PIC is being reset.  Handle it gracefully here
+                */
                atomic_inc(&ps->pit_timer.pending);
+       else if (value > 0)
+               /* in this case, we had multiple outstanding pit interrupts
+                * that we needed to inject.  Reinject
+                */
+               queue_work(ps->pit->wq, &ps->pit->expired);
        ps->irq_ack = 1;
-       raw_spin_unlock(&ps->inject_lock);
+       spin_unlock(&ps->inject_lock);
 }
 
 void __kvm_migrate_pit_timer(struct kvm_vcpu *vcpu)
@@ -264,10 +276,10 @@ void __kvm_migrate_pit_timer(struct kvm_vcpu *vcpu)
                hrtimer_start_expires(timer, HRTIMER_MODE_ABS);
 }
 
-static void destroy_pit_timer(struct kvm_timer *pt)
+static void destroy_pit_timer(struct kvm_pit *pit)
 {
-       pr_debug("execute del timer!\n");
-       hrtimer_cancel(&pt->timer);
+       hrtimer_cancel(&pit->pit_state.pit_timer.timer);
+       cancel_work_sync(&pit->expired);
 }
 
 static bool kpit_is_periodic(struct kvm_timer *ktimer)
@@ -281,6 +293,60 @@ static struct kvm_timer_ops kpit_ops = {
        .is_periodic = kpit_is_periodic,
 };
 
+static void pit_do_work(struct work_struct *work)
+{
+       struct kvm_pit *pit = container_of(work, struct kvm_pit, expired);
+       struct kvm *kvm = pit->kvm;
+       struct kvm_vcpu *vcpu;
+       int i;
+       struct kvm_kpit_state *ps = &pit->pit_state;
+       int inject = 0;
+
+       /* Try to inject pending interrupts when
+        * last one has been acked.
+        */
+       spin_lock(&ps->inject_lock);
+       if (ps->irq_ack) {
+               ps->irq_ack = 0;
+               inject = 1;
+       }
+       spin_unlock(&ps->inject_lock);
+       if (inject) {
+               kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1);
+               kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 0);
+
+               /*
+                * Provides NMI watchdog support via Virtual Wire mode.
+                * The route is: PIT -> PIC -> LVT0 in NMI mode.
+                *
+                * Note: Our Virtual Wire implementation is simplified, only
+                * propagating PIT interrupts to all VCPUs when they have set
+                * LVT0 to NMI delivery. Other PIC interrupts are just sent to
+                * VCPU0, and only if its LVT0 is in EXTINT mode.
+                */
+               if (kvm->arch.vapics_in_nmi_mode > 0)
+                       kvm_for_each_vcpu(i, vcpu, kvm)
+                               kvm_apic_nmi_wd_deliver(vcpu);
+       }
+}
+
+static enum hrtimer_restart pit_timer_fn(struct hrtimer *data)
+{
+       struct kvm_timer *ktimer = container_of(data, struct kvm_timer, timer);
+       struct kvm_pit *pt = ktimer->kvm->arch.vpit;
+
+       if (ktimer->reinject || !atomic_read(&ktimer->pending)) {
+               atomic_inc(&ktimer->pending);
+               queue_work(pt->wq, &pt->expired);
+       }
+
+       if (ktimer->t_ops->is_periodic(ktimer)) {
+               hrtimer_add_expires_ns(&ktimer->timer, ktimer->period);
+               return HRTIMER_RESTART;
+       } else
+               return HRTIMER_NORESTART;
+}
+
 static void create_pit_timer(struct kvm_kpit_state *ps, u32 val, int is_period)
 {
        struct kvm_timer *pt = &ps->pit_timer;
@@ -292,13 +358,13 @@ static void create_pit_timer(struct kvm_kpit_state *ps, u32 val, int is_period)
 
        /* TODO The new value only affected after the retriggered */
        hrtimer_cancel(&pt->timer);
+       cancel_work_sync(&ps->pit->expired);
        pt->period = interval;
        ps->is_periodic = is_period;
 
-       pt->timer.function = kvm_timer_fn;
+       pt->timer.function = pit_timer_fn;
        pt->t_ops = &kpit_ops;
        pt->kvm = ps->pit->kvm;
-       pt->vcpu = pt->kvm->bsp_vcpu;
 
        atomic_set(&pt->pending, 0);
        ps->irq_ack = 1;
@@ -347,7 +413,7 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
                }
                break;
        default:
-               destroy_pit_timer(&ps->pit_timer);
+               destroy_pit_timer(kvm->arch.vpit);
        }
 }
 
@@ -626,7 +692,14 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 
        mutex_init(&pit->pit_state.lock);
        mutex_lock(&pit->pit_state.lock);
-       raw_spin_lock_init(&pit->pit_state.inject_lock);
+       spin_lock_init(&pit->pit_state.inject_lock);
+
+       pit->wq = create_singlethread_workqueue("kvm-pit-wq");
+       if (!pit->wq) {
+               kfree(pit);
+               return NULL;
+       }
+       INIT_WORK(&pit->expired, pit_do_work);
 
        kvm->arch.vpit = pit;
        pit->kvm = kvm;
@@ -685,54 +758,10 @@ void kvm_free_pit(struct kvm *kvm)
                mutex_lock(&kvm->arch.vpit->pit_state.lock);
                timer = &kvm->arch.vpit->pit_state.pit_timer.timer;
                hrtimer_cancel(timer);
+               cancel_work_sync(&kvm->arch.vpit->expired);
                kvm_free_irq_source_id(kvm, kvm->arch.vpit->irq_source_id);
                mutex_unlock(&kvm->arch.vpit->pit_state.lock);
+               destroy_workqueue(kvm->arch.vpit->wq);
                kfree(kvm->arch.vpit);
        }
 }
-
-static void __inject_pit_timer_intr(struct kvm *kvm)
-{
-       struct kvm_vcpu *vcpu;
-       int i;
-
-       kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1);
-       kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 0);
-
-       /*
-        * Provides NMI watchdog support via Virtual Wire mode.
-        * The route is: PIT -> PIC -> LVT0 in NMI mode.
-        *
-        * Note: Our Virtual Wire implementation is simplified, only
-        * propagating PIT interrupts to all VCPUs when they have set
-        * LVT0 to NMI delivery. Other PIC interrupts are just sent to
-        * VCPU0, and only if its LVT0 is in EXTINT mode.
-        */
-       if (kvm->arch.vapics_in_nmi_mode > 0)
-               kvm_for_each_vcpu(i, vcpu, kvm)
-                       kvm_apic_nmi_wd_deliver(vcpu);
-}
-
-void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu)
-{
-       struct kvm_pit *pit = vcpu->kvm->arch.vpit;
-       struct kvm *kvm = vcpu->kvm;
-       struct kvm_kpit_state *ps;
-
-       if (pit) {
-               int inject = 0;
-               ps = &pit->pit_state;
-
-               /* Try to inject pending interrupts when
-                * last one has been acked.
-                */
-               raw_spin_lock(&ps->inject_lock);
-               if (atomic_read(&ps->pit_timer.pending) && ps->irq_ack) {
-                       ps->irq_ack = 0;
-                       inject = 1;
-               }
-               raw_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 900d6b0ba7c2347ed4fb487a92dc3a2d30c83a9f..46d08ca0b48f2a2c3bd04896c1feeb87c3cdef57 100644 (file)
--- a/arch/x86/kvm/i8254.h
+++ b/arch/x86/kvm/i8254.h
@@ -27,7 +27,7 @@ struct kvm_kpit_state {
        u32    speaker_data_on;
        struct mutex lock;
        struct kvm_pit *pit;
-       raw_spinlock_t inject_lock;
+       spinlock_t inject_lock;
        unsigned long irq_ack;
        struct kvm_irq_ack_notifier irq_ack_notifier;
 };
@@ -40,6 +40,8 @@ struct kvm_pit {
        struct kvm_kpit_state pit_state;
        int irq_source_id;
        struct kvm_irq_mask_notifier mask_notifier;
+       struct workqueue_struct *wq;
+       struct work_struct expired;
 };
 
 #define KVM_PIT_BASE_ADDRESS       0x40

diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index 0f4e488331c7aa44b8ad7efc404ebf2b822cdd57..2095a049835e4916b4bd504688e82a2a6cc3796a 100644 (file)
--- a/arch/x86/kvm/irq.c
+++ b/arch/x86/kvm/irq.c
@@ -90,7 +90,6 @@ EXPORT_SYMBOL_GPL(kvm_cpu_get_interrupt);
 void kvm_inject_pending_timer_irqs(struct kvm_vcpu *vcpu)
 {
        kvm_inject_apic_timer_irqs(vcpu);
-       kvm_inject_pit_timer_irqs(vcpu);
        /* TODO: PIT, RTC etc. */
 }
 EXPORT_SYMBOL_GPL(kvm_inject_pending_timer_irqs);