[RFC][PATCH 1/3] Introduce a workqueue to deliver PIT timer interrupts.

Chris Lalancette
2010-06-08T17:57:20Z

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>
---
arch/x86/kvm/i8254.c | 106 ++++++++++++++++++++++++++++++-------------------
arch/x86/kvm/i8254.h | 4 ++
arch/x86/kvm/irq.c | 1 -
arch/x86/kvm/x86.c | 4 ++
4 files changed, 73 insertions(+), 42 deletions(-)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 188d827..dd655ef 100644
--- 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"
@@ -49,6 +50,8 @@
#define RW_STATE_WORD0 3
#define RW_STATE_WORD1 4

+static struct workqueue_struct *pit_wq;
+
/* Compute with 96 bit intermediate result: (a*b)/c */
static u64 muldiv64(u64 a, u32 b, u32 c)
{
@@ -281,6 +284,58 @@ 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.
+ */
+ raw_spin_lock(&ps->inject_lock);
+ if (ps->irq_ack) {
+ ps->irq_ack = 0;
+ inject = 1;
+ }
+ raw_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;
+
+ queue_work(pit_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;
@@ -295,10 +350,9 @@ static void create_pit_timer(struct kvm_kpit_state *ps, u32 val, int is_period)
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;
@@ -628,6 +682,8 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
mutex_lock(&pit->pit_state.lock);
raw_spin_lock_init(&pit->pit_state.inject_lock);

+ INIT_WORK(&pit->expired, pit_do_work);
+
kvm->arch.vpit = pit;
pit->kvm = kvm;

@@ -691,48 +747,16 @@ void kvm_free_pit(struct kvm *kvm)
}
}

-static void __inject_pit_timer_intr(struct kvm *kvm)
+int kvm_pit_create(void)
{
- struct kvm_vcpu *vcpu;
- int i;
+ pit_wq = create_singlethread_workqueue("kvm-pit-wq");
+ if (!pit_wq)
+ return -ENOMEM;

- 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);
+ return 0;
}

-void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu)
+void kvm_pit_cleanup(void)
{
- 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);
- }
+ destroy_workqueue(pit_wq);
}
diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
index 900d6b0..78db13d 100644
--- a/arch/x86/kvm/i8254.h
+++ b/arch/x86/kvm/i8254.h
@@ -40,6 +40,7 @@ struct kvm_pit {
struct kvm_kpit_state pit_state;
int irq_source_id;
struct kvm_irq_mask_notifier mask_notifier;
+ struct work_struct expired;
};

#define KVM_PIT_BASE_ADDRESS 0x40
@@ -55,4 +56,7 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags);
void kvm_free_pit(struct kvm *kvm);
void kvm_pit_reset(struct kvm_pit *pit);

+int kvm_pit_create(void);
+void kvm_pit_cleanup(void);
+
#endif
diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index 0f4e488..2095a04 100644
--- 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);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5fa8684..a8cf1e1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4125,6 +4125,8 @@ int kvm_arch_init(void *opaque)

perf_register_guest_info_callbacks(&kvm_guest_cbs);

+ kvm_pit_create();
+
return 0;

out:
@@ -4133,6 +4135,8 @@ out:

void kvm_arch_exit(void)
{
+ kvm_pit_cleanup();
+
perf_unregister_guest_info_callbacks(&kvm_guest_cbs);

if (!boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
--
1.6.6.1