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

[Jan Kiszka]

On 2011-02-03 08:42, Gleb Natapov wrote:
> On Wed, Feb 02, 2011 at 05:51:32PM +0100, Jan Kiszka wrote:
>>>>>>>> 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?
>>>>>>
>>>>>> 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?
>>>>>>
>>>>> Injection happens by vcpu thread on cpu entry:
>>>>> run->request_interrupt_window = kvm_arch_try_push_interrupts(env);
>>>>> and tpr is synced on vcpu exit, so I do not yet see how what you describe
>>>>> above may happen since during injection vcpu should see correct tpr.
>>>>
>>>> Hmm, maybe this is the key: Once we call into apic_get_interrupt
>>>> (because CPU_INTERRUPT_HARD was set as described above) and we find a
>>>> pending irq below the tpr, we inject a spurious vector instead.
>>>>
>>> That should be easy to verify. I expect Windows to BSOD upon receiving
>>> spurious vector though.
>>
>> I hacked spurious irq injection away, but the issue remains. At the same
>> time, Windows is receiving tons of spurious interrupts without any
>> complaints, even without that tpr optimization in the kernel. So this is
>> obviously not yet the key.
>>
>> Let's try your idea that we miss a wakeup.
>>
> That is unlikely too. If vcpu missed wakeup, "info cpus" would solve the
> hang since it would kick vcpu out of the kernel and missed interrupt would be
> injected on re-entry.

Yeah, and it wouldn't explain the various BSOFs I'm seeing (you get an
even broader spectrum when trying the Windows installations DVDs).

We are probably digging at the wrong site.

Jan

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