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

[Jan Kiszka <jan.kiszka@siemens.com>]

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.

Jan

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