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

["Michael S. Tsirkin" <mst@redhat.com>]

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