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Date: Wed, 02 Feb 2011 17:44:17 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] KVM: Windows 64-bit troubles with user space irqchip
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: kvm <kvm@vger.kernel.org>, Gleb Natapov <gleb@redhat.com>, qemu-devel <qemu-devel@nongnu.org>

On 02/02/2011 05:35 PM, Jan Kiszka wrote:
> >
> >  And yet, both are synchronized via qemu_mutex.  So we're still missing
> >  something in this picture.
> >
> >>  Run apic_set_irq on the vcpu?
> >
> >  static void apic_set_irq(APICState *s, int vector_num, int trigger_mode)
> >  {
> >       apic_irq_delivered += !get_bit(s->irr, vector_num);
> >
> >       trace_apic_set_irq(apic_irq_delivered);
> >
> >       set_bit(s->irr, vector_num);
> >
> >  This is even more async with kernel irqchip
> >
> >       if (trigger_mode)
> >           set_bit(s->tmr, vector_num);
> >       else
> >           reset_bit(s->tmr, vector_num);
> >
> >  This is protected by qemu_mutex
> >
> >       apic_update_irq(s);
> >
> >  This will be run the next time the vcpu exits, via apic_get_interrupt().
>
> The decision to pend an IRQ (and potentially kick the vcpu) takes place
> immediately in acip_update_irq. And it is based on current irr as well
> as tpr. But we update again when user space returns with a new value.

Right.  My current understanding is that it is correct.  But I 
distinctly remember that I came to a different conclusion when the 
failure first occurred (and the conclusion was that the patch did not 
cause the problem, just made it much more likely to see a not-up-to-date 
TPR).

> >
> >  }
> >
> >  Did you check whether reverting that commit helps?
> >
>
> Just did so, and I can no longer reproduce the problem. Hmm...

At least we have a pointer.

-- 
error compiling committee.c: too many arguments to function