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 Userspace APIC is broken since it may run with an outdated cr8, does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...
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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