Re: NetBSD dom0 PVH: hardware interrupts stalls

["Jürgen Groß" <jgross@suse.com>]

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On 27.11.20 14:40, Jan Beulich wrote:
> On 27.11.2020 14:31, Manuel Bouyer wrote:
>> On Fri, Nov 27, 2020 at 02:18:54PM +0100, Jan Beulich wrote:
>>> On 27.11.2020 14:13, Manuel Bouyer wrote:
>>>> On Fri, Nov 27, 2020 at 12:29:35PM +0100, Jan Beulich wrote:
>>>>> On 27.11.2020 11:59, Roger Pau Monné wrote:
>>>>>> --- a/xen/arch/x86/hvm/irq.c
>>>>>> +++ b/xen/arch/x86/hvm/irq.c
>>>>>> @@ -187,6 +187,10 @@ void hvm_gsi_assert(struct domain *d, unsigned int gsi)
>>>>>>        * to know if the GSI is pending or not.
>>>>>>        */
>>>>>>       spin_lock(&d->arch.hvm.irq_lock);
>>>>>> +    if ( gsi == TRACK_IRQ )
>>>>>> +        debugtrace_printk("hvm_gsi_assert irq %u trig %u assert count %u\n",
>>>>>> +                          gsi, trig, hvm_irq->gsi_assert_count[gsi]);
>>>>>
>>>>> This produces
>>>>>
>>>>> 81961 hvm_gsi_assert irq 34 trig 1 assert count 1
>>>>>
>>>>> Since the logging occurs ahead of the call to assert_gsi(), it
>>>>> means we don't signal anything to Dom0, because according to our
>>>>> records there's still an IRQ in flight. Unfortunately we only
>>>>> see the tail of the trace, so it's not possible to tell how / when
>>>>> we got into this state.
>>>>>
>>>>> Manuel - is this the only patch you have in place? Or did you keep
>>>>> any prior ones? Iirc there once was one where Roger also suppressed
>>>>> some de-assert call.
>>>>
>>>> Yes, I have some of the previous patches (otherwise Xen panics).
>>>> Attached is the diffs I currently have
>>>
>>> I think you want to delete the hunk dropping the call to
>>> hvm_gsi_deassert() from pt_irq_time_out(). Iirc it was that
>>> addition which changed the behavior to just a single IRQ ever
>>> making it into Dom0. And it ought to be only the change to
>>> msix_write() which is needed to avoid the panic.
>>
>> yes, I did keep the hvm_gsi_deassert() patch because I expected it
>> to make things easier, as it allows to interract with Xen without changing
>> interrupt states.
> 
> Right, but then we'd need to see the beginning of the trace,
> rather than it starting at (in this case) about 95,000. Yet ...
> 
>> I removed it, here's a new trace
>>
>> http://www-soc.lip6.fr/~bouyer/xen-log12.txt
> 
> ... hmm, odd - no change at all:
> 
> 95572 hvm_gsi_assert irq 34 trig 1 assert count 1
> 
> I was sort of expecting that this might be where we fail to
> set the assert count back to zero. Will need further
> thinking, if nothing else than how to turn down the verbosity
> without hiding crucial information. Or maybe Roger has got
> some idea ...

Set debugtrace buffer size to something huge?

Panic when the buffer is full?

It should be noted that the debugtrace in being printed in case of a
panic.


Juergen


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