Re: NetBSD dom0 PVH: hardware interrupts stalls

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.11.2020 11:05, Jan Beulich wrote:
> On 23.11.2020 18:39, Manuel Bouyer wrote:
>> On Mon, Nov 23, 2020 at 06:06:10PM +0100, Roger Pau Monné wrote:
>>> OK, I'm afraid this is likely too verbose and messes with the timings.
>>>
>>> I've been looking (again) into the code, and I found something weird
>>> that I think could be related to the issue you are seeing, but haven't
>>> managed to try to boot the NetBSD kernel provided in order to assert
>>> whether it solves the issue or not (or even whether I'm able to
>>> repro it). Would you mind giving the patch below a try?
>>
>> With this, I get the same hang but XEN outputs don't wake up the interrupt
>> any more. The NetBSD counter shows only one interrupt for ioapic2 pin 2,
>> while I would have about 8 at the time of the hang.
>>
>> So, now it looks like interrupts are blocked forever.
> 
> Which may be a good thing for debugging purposes, because now we have
> a way to investigate what is actually blocking the interrupt's
> delivery without having to worry about more output screwing the
> overall picture.
> 
>> At
>> http://www-soc.lip6.fr/~bouyer/xen-log5.txt
>> you'll find the output of the 'i' key.
> 
> (XEN)    IRQ:  34 vec:59 IO-APIC-level   status=010 aff:{0}/{0-7} in-flight=1 
> d0: 34(-MM)
> 
> (XEN)     IRQ 34 Vec 89:
> (XEN)       Apic 0x02, Pin  2: vec=59 delivery=LoPri dest=L status=1 
> polarity=1 irr=1 trig=L mask=0 dest_id:00000001

Since it repeats in Manuel's latest dump, perhaps the odd combination
of status=1 and irr=1 is to tell us something? It is my understanding
that irr ought to become set only when delivery-status clears. Yet I
don't know what to take from this...

Jan