Re: [PATCH v8 1/6] kvm: Allow filtering of acked irqs

Alex Williamson
2012-08-15T16:47:41Z

On Wed, 2012-08-15 at 15:27 +0300, Michael S. Tsirkin wrote:
> On Fri, Aug 10, 2012 at 04:37:17PM -0600, Alex Williamson wrote:
> > Registering an kvm_irq_ack_notifier with kian.irq_source_id < 0
> > retains existing behavior, filling in the actual irq_source_id results
> > in the callback only being called when the specified irq_source_id is
> > asserting the given gsi.
> >
> > The i8254 PIT remains unfiltered because it de-asserts it's irq source
> > id, so it's notifier would never get called otherwise. KVM device
> > assignment gets filtering as it de-asserts the GSI in it's notifier.
> >
> > Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
>
> Looks good to me. For the record, I expect this to help if
> - an assigned device interrupt is shared in host
> so we use slow config cycles in the ack notifier
> - said device is sharing interrupt with another device in guest
> - said another device is actually driving most interrupts
> For example, I think this could be tested
> by booting guest with pci=nomsi.

Yes, that's how I do most of my testing of legacy interrupts with
vfio-pci. KVM assignment is smart enough not to do config access unless
the irq is marked as disabled, but it does eliminate an unnecessary
de-assert and a couple spinlocks in assignment code.

> A minor suggestions below but
> nothing that needs to block this patch.
>
> > ---
> >
> > arch/x86/kvm/i8254.c | 1 +
> > arch/x86/kvm/i8259.c | 8 +++++++-
> > include/linux/kvm_host.h | 4 +++-
> > virt/kvm/assigned-dev.c | 1 +
> > virt/kvm/ioapic.c | 5 ++++-
> > virt/kvm/irq_comm.c | 6 ++++--
> > 6 files changed, 20 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
> > index adba28f..2355d19 100644
> > --- a/arch/x86/kvm/i8254.c
> > +++ b/arch/x86/kvm/i8254.c
> > @@ -709,6 +709,7 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
> > 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_source_id = -1; /* No filter */
>
> A bit prettier would be to
> #define KVM_NO_IRQ_SOURCE_ID (-1)
> and test for it explicitly.

Ok. I'll add a define and resend this one. Thanks,

Alex

> > 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;
> > diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
> > index e498b18..d2175a9 100644
> > --- a/arch/x86/kvm/i8259.c
> > +++ b/arch/x86/kvm/i8259.c
> > @@ -74,9 +74,14 @@ static void pic_unlock(struct kvm_pic *s)
> >
> > static void pic_clear_isr(struct kvm_kpic_state *s, int irq)
> > {
> > + unsigned long irq_source_ids;
> > +
> > s->isr &= ~(1 << irq);
> > if (s != &s->pics_state->pics[0])
> > irq += 8;
> > +
> > + irq_source_ids = s->pics_state->irq_states[irq];
> > +
> > /*
> > * We are dropping lock while calling ack notifiers since ack
> > * notifier callbacks for assigned devices call into PIC recursively.
> > @@ -84,7 +89,8 @@ static void pic_clear_isr(struct kvm_kpic_state *s, int irq)
> > * it should be safe since PIC state is already updated at this stage.
> > */
> > pic_unlock(s->pics_state);
> > - kvm_notify_acked_irq(s->pics_state->kvm, SELECT_PIC(irq), irq);
> > + kvm_notify_acked_irq(s->pics_state->kvm, SELECT_PIC(irq), irq,
> > + irq_source_ids);
> > pic_lock(s->pics_state);
> > }
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index b70b48b..2ad3e4a 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -577,6 +577,7 @@ int kvm_is_mmio_pfn(pfn_t pfn);
> >
> > struct kvm_irq_ack_notifier {
> > struct hlist_node link;
> > + int irq_source_id;
> > unsigned gsi;
> > void (*irq_acked)(struct kvm_irq_ack_notifier *kian);
> > };
> > @@ -627,7 +628,8 @@ void kvm_get_intr_delivery_bitmask(struct kvm_ioapic *ioapic,
> > int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level);
> > int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
> > int irq_source_id, int level);
> > -void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin);
> > +void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin,
> > + unsigned long irq_source_ids);
> > void kvm_register_irq_ack_notifier(struct kvm *kvm,
> > struct kvm_irq_ack_notifier *kian);
> > void kvm_unregister_irq_ack_notifier(struct kvm *kvm,
> > diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> > index 23a41a9..a08c9c1 100644
> > --- a/virt/kvm/assigned-dev.c
> > +++ b/virt/kvm/assigned-dev.c
> > @@ -407,6 +407,7 @@ static int assigned_device_enable_guest_intx(struct kvm *kvm,
> > {
> > dev->guest_irq = irq->guest_irq;
> > dev->ack_notifier.gsi = irq->guest_irq;
> > + dev->ack_notifier.irq_source_id = dev->irq_source_id;
> > return 0;
> > }
> >
> > diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
> > index ef61d52..1a9f445 100644
> > --- a/virt/kvm/ioapic.c
> > +++ b/virt/kvm/ioapic.c
> > @@ -241,10 +241,12 @@ static void __kvm_ioapic_update_eoi(struct kvm_ioapic *ioapic, int vector,
> >
> > for (i = 0; i < IOAPIC_NUM_PINS; i++) {
> > union kvm_ioapic_redirect_entry *ent = &ioapic->redirtbl[i];
> > + unsigned long irq_source_ids;
> >
> > if (ent->fields.vector != vector)
> > continue;
> >
> > + irq_source_ids = ioapic->irq_states[i];
> > /*
> > * We are dropping lock while calling ack notifiers because ack
> > * notifier callbacks for assigned devices call into IOAPIC
> > @@ -254,7 +256,8 @@ static void __kvm_ioapic_update_eoi(struct kvm_ioapic *ioapic, int vector,
> > * after ack notifier returns.
> > */
> > spin_unlock(&ioapic->lock);
> > - kvm_notify_acked_irq(ioapic->kvm, KVM_IRQCHIP_IOAPIC, i);
> > + kvm_notify_acked_irq(ioapic->kvm, KVM_IRQCHIP_IOAPIC, i,
> > + irq_source_ids);
> > spin_lock(&ioapic->lock);
> >
> > if (trigger_mode != IOAPIC_LEVEL_TRIG)
> > diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> > index 83402d7..7d75126 100644
> > --- a/virt/kvm/irq_comm.c
> > +++ b/virt/kvm/irq_comm.c
> > @@ -173,7 +173,8 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level)
> > return ret;
> > }
> >
> > -void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
> > +void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin,
> > + unsigned long irq_source_ids)
> > {
> > struct kvm_irq_ack_notifier *kian;
> > struct hlist_node *n;
> > @@ -186,7 +187,8 @@ void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
> > if (gsi != -1)
> > hlist_for_each_entry_rcu(kian, n, &kvm->irq_ack_notifier_list,
> > link)
> > - if (kian->gsi == gsi)
> > + if (kian->gsi == gsi && (kian->irq_source_id < 0 ||
> > + test_bit(kian->irq_source_id, &irq_source_ids)))
> > kian->irq_acked(kian);
> > rcu_read_unlock();
> > }
>