Re: [Qemu-devel] [question] e1000 interrupt storm happenedbecauseofits correspondingioapic->irr bit always set

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

On Thu, Aug 28, 2014 at 08:55:18PM +0800, Zhang Haoyu wrote:
> Hi Jason,
> I tested below patch, it's okay, the e1000 interrupt storm disappeared.
> But I am going to make a bit change on it, could you help review it?
> 
> >Currently, we call ioapic_service() immediately when we find the irq is still
> >active during eoi broadcast. But for real hardware, there's some dealy between
> >the EOI writing and irq delivery (system bus latency?). So we need to emulate
> >this behavior. Otherwise, for a guest who haven't register a proper irq handler
> >, it would stay in the interrupt routine as this irq would be re-injected
> >immediately after guest enables interrupt. This would lead guest can't move
> >forward and may miss the possibility to get proper irq handler registered (one
> >example is windows guest resuming from hibernation).
> >
> >As there's no way to differ the unhandled irq from new raised ones, this patch
> >solve this problems by scheduling a delayed work when the count of irq injected
> >during eoi broadcast exceeds a threshold value. After this patch, the guest can
> >move a little forward when there's no suitable irq handler in case it may
> >register one very soon and for guest who has a bad irq detection routine ( such
> >as note_interrupt() in linux ), this bad irq would be recognized soon as in the
> >past.
> >
> >Signed-off-by: Jason Wang <jasowang <at> redhat.com>
> >---
> > virt/kvm/ioapic.c |   47 +++++++++++++++++++++++++++++++++++++++++++++--
> > virt/kvm/ioapic.h |    2 ++
> > 2 files changed, 47 insertions(+), 2 deletions(-)
> >
> >diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
> >index dcaf272..892253e 100644
> >--- a/virt/kvm/ioapic.c
> >+++ b/virt/kvm/ioapic.c
> > <at>  <at>  -221,6 +221,24  <at>  <at>  int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int level)
> > 	return ret;
> > }
> >
> >+static void kvm_ioapic_eoi_inject_work(struct work_struct *work)
> >+{
> >+	int i, ret;
> >+	struct kvm_ioapic *ioapic = container_of(work, struct kvm_ioapic,
> >+						 eoi_inject.work);
> >+	spin_lock(&ioapic->lock);
> >+	for (i = 0; i < IOAPIC_NUM_PINS; i++) {
> >+		union kvm_ioapic_redirect_entry *ent = &ioapic->redirtbl[i];
> >+
> >+		if (ent->fields.trig_mode != IOAPIC_LEVEL_TRIG)
> >+			continue;
> >+
> >+		if (ioapic->irr & (1 << i) && !ent->fields.remote_irr)
> >+			ret = ioapic_service(ioapic, i);
> >+	}
> >+	spin_unlock(&ioapic->lock);
> >+}
> >+
> > static void __kvm_ioapic_update_eoi(struct kvm_ioapic *ioapic, int vector,
> > 				     int trigger_mode)
> > {
> > <at>  <at>  -249,8 +267,29  <at>  <at>  static void __kvm_ioapic_update_eoi(struct kvm_ioapic *ioapic, int vector,
> >
> > 		ASSERT(ent->fields.trig_mode == IOAPIC_LEVEL_TRIG);
> > 		ent->fields.remote_irr = 0;
> >-		if (!ent->fields.mask && (ioapic->irr & (1 << i)))
> >-			ioapic_service(ioapic, i);
> >+		if (!ent->fields.mask && (ioapic->irr & (1 << i))) {
> >+			++ioapic->irq_eoi;
> -+			++ioapic->irq_eoi;
> ++		    ++ioapic->irq_eoi[i];
> >+			if (ioapic->irq_eoi == 100) {
> -+			if (ioapic->irq_eoi == 100) {
> ++			if (ioapic->irq_eoi[i] == 100) {
> >+				/*
> >+				 * Real hardware does not deliver the irq so
> >+				 * immediately during eoi broadcast, so we need
> >+				 * to emulate this behavior. Otherwise, for
> >+				 * guests who has not registered handler of a
> >+				 * level irq, this irq would be injected
> >+				 * immediately after guest enables interrupt
> >+				 * (which happens usually at the end of the
> >+				 * common interrupt routine). This would lead
> >+				 * guest can't move forward and may miss the
> >+				 * possibility to get proper irq handler
> >+				 * registered. So we need to give some breath to
> >+				 * guest. TODO: 1 is too long?
> >+				 */
> >+				schedule_delayed_work(&ioapic->eoi_inject, 1);
> >+				ioapic->irq_eoi = 0;
> -+				ioapic->irq_eoi = 0;
> ++				ioapic->irq_eoi[i] = 0;
> >+			} else {
> >+				ioapic_service(ioapic, i);
> >+			}
> >+		}
> ++		else {
> ++			ioapic->irq_eoi[i] = 0;
> ++		}
> > 	}
> > }
> I think ioapic->irq_eoi is prone to reach to 100, because during a eoi broadcast, 
> it's possible that another interrupt's (not current eoi's corresponding interrupt) irr is set, so the ioapic->irq_eoi will grow continually,
> and not too long, ioapic->irq_eoi will reach to 100.
> I want to add "u32 irq_eoi[IOAPIC_NUM_PINS];" instead of "u32 irq_eoi;".
> Any ideas?
> 
> Zhang Haoyu

I'm a bit concerned how this will affect realtime guests.
Worth adding a flag to enable this, so that e.g. virtio is not
affected?


> >
> > <at>  <at>  -375,12 +414,14  <at>  <at>  void kvm_ioapic_reset(struct kvm_ioapic *ioapic)
> > {
> > 	int i;
> >
> >+	cancel_delayed_work_sync(&ioapic->eoi_inject);
> > 	for (i = 0; i < IOAPIC_NUM_PINS; i++)
> > 		ioapic->redirtbl[i].fields.mask = 1;
> > 	ioapic->base_address = IOAPIC_DEFAULT_BASE_ADDRESS;
> > 	ioapic->ioregsel = 0;
> > 	ioapic->irr = 0;
> > 	ioapic->id = 0;
> >+	ioapic->irq_eoi = 0;
> -+	ioapic->irq_eoi = 0;
> ++	memset(ioapic->irq_eoi, 0x00, IOAPIC_NUM_PINS);
> > 	update_handled_vectors(ioapic);
> > }
> >
> > <at>  <at>  -398,6 +439,7  <at>  <at>  int kvm_ioapic_init(struct kvm *kvm)
> > 	if (!ioapic)
> > 		return -ENOMEM;
> > 	spin_lock_init(&ioapic->lock);
> >+	INIT_DELAYED_WORK(&ioapic->eoi_inject, kvm_ioapic_eoi_inject_work);
> > 	kvm->arch.vioapic = ioapic;
> > 	kvm_ioapic_reset(ioapic);
> > 	kvm_iodevice_init(&ioapic->dev, &ioapic_mmio_ops);
> > <at>  <at>  -418,6 +460,7  <at>  <at>  void kvm_ioapic_destroy(struct kvm *kvm)
> > {
> > 	struct kvm_ioapic *ioapic = kvm->arch.vioapic;
> >
> >+	cancel_delayed_work_sync(&ioapic->eoi_inject);
> > 	if (ioapic) {
> > 		kvm_io_bus_unregister_dev(kvm, KVM_MMIO_BUS, &ioapic->dev);
> > 		kvm->arch.vioapic = NULL;
> >diff --git a/virt/kvm/ioapic.h b/virt/kvm/ioapic.h
> >index 0b190c3..8938e66 100644
> >--- a/virt/kvm/ioapic.h
> >+++ b/virt/kvm/ioapic.h
> > <at>  <at>  -47,6 +47,8  <at>  <at>  struct kvm_ioapic {
> > 	void (*ack_notifier)(void *opaque, int irq);
> > 	spinlock_t lock;
> > 	DECLARE_BITMAP(handled_vectors, 256);
> >+	struct delayed_work eoi_inject;
> >+	u32 irq_eoi;
> -+	u32 irq_eoi;
> ++	u32 irq_eoi[IOAPIC_NUM_PINS];
> > };
> >
> > #ifdef DEBUG
>