On Mon, Aug 24, 2009 at 08:16:46PM +0300, Gleb Natapov wrote:
> On Mon, Aug 24, 2009 at 01:32:56PM -0300, Marcelo Tosatti wrote:
> > On Mon, Aug 24, 2009 at 03:06:23PM +0300, Gleb Natapov wrote:
> > > Use return value from kvm_set_irq() to track coalesced PIT interrupts
> > > instead of ack/mask notifiers.
> >
> > Gleb,
> >
> > What is the advantage of doing so?
> >
> Current code very fragile and relies on hacks to work. Lets take calling
> of ack notifiers on pic reset as an example. Why is it needed?
To signal the ack notifiers users that, in case of reset with pending
IRR, the given interrupt has been "acked" (its an artificial ack event).
Is there a need to differentiate between actual interrupt ack and reset
with pending IRR? At the time this code was written, there was no
indication that differentation would be necessary.
> It is obviously wrong thing to do from assigned devices POV.
Thats not entirely clear to me. So what happens if a guest with PIC
assigned device resets with a pending IRR? The host interrupt line will
be kept disabled, even though the guest is able to process further
interrupts?
> Why ioapic calls mask notifiers but pic doesn't?
Because it is not implemented.
> Besides diffstat for the patch shows:
> 2 files changed, 16 insertions(+), 59 deletions(-)
>
> 43 lines less for the same functionality. Looks like clear win to me.
>
> > Ack notifiers are asynchronous notifications. Using the return value
> > from kvm_set_irq implies that timer emulation is based on a "tick
> > generating device" on the host side.
> No notification is needed in the first place. You know immediately
> if injection fails or not. I don't see why "using return value from
> kvm_set_irq implies that timer emulation is based on a "tick generating
> device" on the host side"? What can you do with ack notifiers that can't
> be done without?
If you don't have a host timer emulating the guest PIT, to periodically
bang on kvm_set_irq, how do you know when to attempt reinjection?
You keep calling kvm_set_irq on every guest entry to figure out when
reinjection is possible?
> > What I mean is that the ack notifications are useful, since they are
> > asynchronous.
> >
> What I mean is that no notification is needed at all since result is
> known immediately.
?
> > Supposing your goal is to get rid of ack notifiers, due to their burden
> > in irqchip code?
> >
> Unfortunately to get rid of ack notifiers we need to get rid of assigned
> devices. I will gladly do that, but I doubt Avi shares my enthusiasm.
> The patch to remove mask notification already sits in my patch queue though.
>
> > > Signed-off-by: Gleb Natapov <gleb@xxxxxxxxxx>
> > > diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
> > > index b857ca3..0b63991 100644
> > > --- a/arch/x86/kvm/i8254.c
> > > +++ b/arch/x86/kvm/i8254.c
> > > @@ -231,20 +231,7 @@ int pit_has_pending_timer(struct kvm_vcpu *vcpu)
> > > {
> > > struct kvm_pit *pit = vcpu->kvm->arch.vpit;
> > >
> > > - if (pit && kvm_vcpu_is_bsp(vcpu) && pit->pit_state.irq_ack)
> > > - return atomic_read(&pit->pit_state.pit_timer.pending);
> > > - return 0;
> > > -}
> > > -
> > > -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);
> > > - spin_lock(&ps->inject_lock);
> > > - if (atomic_dec_return(&ps->pit_timer.pending) < 0)
> > > - atomic_inc(&ps->pit_timer.pending);
> > > - ps->irq_ack = 1;
> > > - spin_unlock(&ps->inject_lock);
> > > + return atomic_read(&pit->pit_state.pit_timer.pending);
> > > }
> > >
> > > void __kvm_migrate_pit_timer(struct kvm_vcpu *vcpu)
> > > @@ -297,7 +284,6 @@ static void create_pit_timer(struct kvm_kpit_state *ps, u32 val, int is_period)
> > > pt->vcpu = pt->kvm->bsp_vcpu;
> > >
> > > atomic_set(&pt->pending, 0);
> > > - ps->irq_ack = 1;
> > >
> > > hrtimer_start(&pt->timer, ktime_add_ns(ktime_get(), interval),
> > > HRTIMER_MODE_ABS);
> > > @@ -577,17 +563,6 @@ 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.irq_ack = 1;
> > > -}
> > > -
> > > -static void pit_mask_notifer(struct kvm_irq_mask_notifier *kimn, bool mask)
> > > -{
> > > - struct kvm_pit *pit = container_of(kimn, struct kvm_pit, mask_notifier);
> > > -
> > > - if (!mask) {
> > > - atomic_set(&pit->pit_state.pit_timer.pending, 0);
> > > - pit->pit_state.irq_ack = 1;
> > > - }
> > > }
> > >
> > > static const struct kvm_io_device_ops pit_dev_ops = {
> > > @@ -619,7 +594,6 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
> > >
> > > mutex_init(&pit->pit_state.lock);
> > > mutex_lock(&pit->pit_state.lock);
> > > - spin_lock_init(&pit->pit_state.inject_lock);
> > >
> > > kvm->arch.vpit = pit;
> > > pit->kvm = kvm;
> > > @@ -628,17 +602,11 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
> > > 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);
> > > pit_state->pit_timer.reinject = true;
> > > mutex_unlock(&pit->pit_state.lock);
> > >
> > > kvm_pit_reset(pit);
> > >
> > > - pit->mask_notifier.func = pit_mask_notifer;
> > > - kvm_register_irq_mask_notifier(kvm, 0, &pit->mask_notifier);
> > > -
> > > kvm_iodevice_init(&pit->dev, &pit_dev_ops);
> > > ret = __kvm_io_bus_register_dev(&kvm->pio_bus, &pit->dev);
> > > if (ret < 0)
> > > @@ -670,10 +638,6 @@ void kvm_free_pit(struct kvm *kvm)
> > > struct hrtimer *timer;
> > >
> > > if (kvm->arch.vpit) {
> > > - kvm_unregister_irq_mask_notifier(kvm, 0,
> > > - &kvm->arch.vpit->mask_notifier);
> > > - kvm_unregister_irq_ack_notifier(kvm,
> > > - &kvm->arch.vpit->pit_state.irq_ack_notifier);
> > > mutex_lock(&kvm->arch.vpit->pit_state.lock);
> > > timer = &kvm->arch.vpit->pit_state.pit_timer.timer;
> > > hrtimer_cancel(timer);
> > > @@ -683,12 +647,12 @@ void kvm_free_pit(struct kvm *kvm)
> > > }
> > > }
> > >
> > > -static void __inject_pit_timer_intr(struct kvm *kvm)
> > > +static int __inject_pit_timer_intr(struct kvm *kvm)
> > > {
> > > struct kvm_vcpu *vcpu;
> > > - int i;
> > > + int i, r;
> > >
> > > - kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1);
> > > + r = kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1);
> > > kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 0);
> > >
> > > /*
> > > @@ -703,6 +667,8 @@ static void __inject_pit_timer_intr(struct kvm *kvm)
> > > if (kvm->arch.vapics_in_nmi_mode > 0)
> > > kvm_for_each_vcpu(i, vcpu, kvm)
> > > kvm_apic_nmi_wd_deliver(vcpu);
> > > +
> > > + return r;
> > > }
> > >
> > > void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu)
> > > @@ -711,20 +677,14 @@ void kvm_inject_pit_timer_irqs(struct kvm_vcpu *vcpu)
> > > 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.
> > > - */
> > > - 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);
> > > - }
> > > + if (!pit)
> > > + return;
> > > +
> > > + ps = &pit->pit_state;
> > > +
> > > + if (!atomic_read(&ps->pit_timer.pending))
> > > + return;
> > > +
> > > + if (__inject_pit_timer_intr(kvm))
> > > + atomic_dec(&ps->pit_timer.pending);
> > > }
> > > diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
> > > index d4c1c7f..19937da 100644
> > > --- a/arch/x86/kvm/i8254.h
> > > +++ b/arch/x86/kvm/i8254.h
> > > @@ -28,8 +28,6 @@ struct kvm_kpit_state {
> > > struct mutex lock;
> > > struct kvm_pit *pit;
> > > spinlock_t inject_lock;
> > > - unsigned long irq_ack;
> > > - struct kvm_irq_ack_notifier irq_ack_notifier;
> > > };
> > >
> > > struct kvm_pit {
> > > @@ -39,7 +37,6 @@ struct kvm_pit {
> > > struct kvm *kvm;
> > > struct kvm_kpit_state pit_state;
> > > int irq_source_id;
> > > - struct kvm_irq_mask_notifier mask_notifier;
> > > };
> > >
> > > #define KVM_PIT_BASE_ADDRESS 0x40
> > > --
> > > Gleb.
>
> --
> Gleb.
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