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

Michael S. Tsirkin
2012-08-15T12:26:06Z

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.

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.

> 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();
> }

--
MST