Re: [Qemu-devel] KVM: Windows 64-bit troubles with user space irqchip

[Avi Kivity <avi@redhat.com>]

On 02/03/2011 11:32 AM, Jan Kiszka wrote:
> On 2011-02-03 09:18, Avi Kivity wrote:
> >  On 02/02/2011 05:52 PM, Jan Kiszka wrote:
> >>>>
> >>>   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?
> >>
> >>  I'm not yet confident about the logic of the kernel patch: mov to cr8 is
> >>  serializing. If the guest raises the tpr and then signals this with a
> >>  succeeding, non vm-exiting instruction to the other vcpus, one of those
> >>  could inject an interrupt with a higher priority than the previous tpr,
> >>  but a lower one than current tpr. QEMU user space would accept this
> >>  interrupt - and would likely surprise the guest. Do I miss something?
> >
> >  apic_get_interrupt() is only called from the vcpu thread, so it should
> >  see a correct tpr.
> >
> >  The only difference I can see with the patch is that we may issue a
> >  spurious cpu_interrupt().  But that shouldn't do anything bad, should it?
>
> I tested this yesterday, and it doesn't confuse Windows. It actually
> receives quite a few spurious IRQs in normal operation, w/ or w/o the
> kernel's tpr optimization.

I don't see why there should be any spurious interrupts in normal 
operation.  From the docs, these happen due to an INTA cycle racing with 
raising the TPR, but in ioapic mode, there shouldn't be any INTA cycles.

-- 
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