On Wed, Feb 02, 2011 at 04:35:25PM +0100, Jan Kiszka wrote:
> On 2011-02-02 16:09, Avi Kivity wrote:
> > On 02/02/2011 04:52 PM, Jan Kiszka wrote:
> >> On 2011-02-02 15:43, Jan Kiszka wrote:
> >>> On 2011-02-02 15:35, Avi Kivity wrote:
> >>>> On 02/02/2011 04:30 PM, Jan Kiszka wrote:
> >>>>> On 2011-02-02 14:05, Avi Kivity wrote:
> >>>>>> On 02/02/2011 02:50 PM, Jan Kiszka wrote:
> >>>>>>>>>
> >>>>>>>> Opps, -smp 1. With -smp 2 it boot almost completely and then hangs.
> >>>>>>>
> >>>>>>> Ah, good (or not good). With Windows 2003 Server, I actually get a Blue
> >>>>>>> Screen (Stop 0x000000b8).
> >>>>>>
> >>>>>> Userspace APIC is broken since it may run with an outdated cr8, does
> >>>>>> reverting 27a4f7976d5 help?
> >>>>>
> >>>>> Can you elaborate on what is broken? The way hw/apic.c maintains the
> >>>>> tpr? Would it make sense to compare this against the in-kernel model? Or
> >>>>> do you mean something else?
> >>>>
> >>>> The problem, IIRC, was that we look up the TPR but it may already have
> >>>> been changed by the running vcpu. Not 100% sure.
> >>>>
> >>>> If that is indeed the problem then the fix would be to process the APIC
> >>>> in vcpu context (which is what the kernel does - we set a bit in the IRR
> >>>> and all further processing is synchronous).
> >>>
> >>> You mean: user space changes the tpr value while the vcpu is in KVM_RUN,
> >>> then we return from the kernel and overwrite the tpr in the apic with
> >>> the vcpu's view, right?
> >>
> >> Hmm, probably rather that there is a discrepancy between tpr and irr.
> >> The latter is changed asynchronously /wrt to the vcpu, the former /wrt
> >> the user space device model.
> >
> > 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.
>
> >
> > }
> >
> > Did you check whether reverting that commit helps?
> >
>
> Just did so, and I can no longer reproduce the problem. Hmm...
>
If there is no problem in the logic of this commit (and I do not see
one yet) then we somewhere miss kicking vcpu when interrupt, that should be
handled, arrives?
--
Gleb.
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