Re: NetBSD dom0 PVH: hardware interrupts stalls

[Manuel Bouyer <bouyer@antioche.eu.org>]

On Wed, Nov 18, 2020 at 09:57:38AM +0100, Roger Pau Monné wrote:
> On Tue, Nov 17, 2020 at 05:40:33PM +0100, Manuel Bouyer wrote:
> > On Tue, Nov 17, 2020 at 04:58:07PM +0100, Roger Pau Monné wrote:
> > > [...]
> > > 
> > > I have attached a patch below that will dump the vIO-APIC info as part
> > > of the 'i' debug key output, can you paste the whole output of the 'i'
> > > debug key when the system stalls?
> > 
> > see attached file. Note that the kernel did unstall while 'i' output was
> > being printed, so it is mixed with some NetBSD kernel output.
> > The idt entry of the 'ioapic2 pin2' interrupt is 103 on CPU 0.
> > 
> > I also put the whole sequence at
> > http://www-soc.lip6.fr/~bouyer/xen-log3.txt
> 
> On one of the instances the pin shows up as masked, but I'm not sure
> if that's relevant since later it shows up as unmasked. Might just be
> part of how NetBSD handles such interrupts.

Yes, NetBSD can mask an interrupt source if the interrupts needs to be delayed.
It will be unmasked once the interrupt has been handled.

Would it be possible that Xen misses an unmask write, or fails to
call the vector if the interrupt is again pending at the time of the
unmask ?


> [...]
> On a maybe unrelated question, how do you setup the event channel
> callback, is it using HVM_PARAM_CALLBACK_IRQ and
> HVM_PARAM_CALLBACK_TYPE_VECTOR?

Yes, the code is at
https://github.com/NetBSD/src/blob/f9a54eaecfb47bce597f72f6cae8861f4d486eb4/sys/arch/xen/xen/hypervisor.c#L457

> 
> Are you EOI'ing such vector on the local APIC when servicing the
> interrupt?

I think it's OK. the code is at
https://github.com/NetBSD/src/blob/f9a54eaecfb47bce597f72f6cae8861f4d486eb4/sys/arch/amd64/amd64/vector.S#L770

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--