Re: [Xen-devel] HPET interrupt remapping during boot

[Jan Beulich <jbeulich@xxxxxxxx>]

On 09.10.2019 12:11, Roger Pau Monné  wrote:
> And it does print the following when setting up the iommu:
> 
> (XEN) ioapic 0 pin 0 not masked
> (XEN) vec=00 delivery=ExINT dest=P status=0 polarity=0 irr=0 trig=E mask=0 
> dest_id:00010000
> 
> I wonder, shouldn't all pins of all the io-apics be masked at boot?

I think you might get different answers here depending on whether
you ask firmware or OS people. In fact there are cases where the
IO-APIC needs to be left in this state, I think, but such would
likely need properly reflecting in ACPI tables (albeit I don't
know/recall how this would be done; looking at the code ). This goes back to 
times
when IO-APICs were new and OSes would not even know about them,
yet they wouldn't get any interrupts to work if fiddling with
only the PIC (sitting behind IO-APIC pin 0).

See enable_IO_APIC(), where we actually use this property to
determine the pin behind which the 8259 sits.

I've seen quite many systems where in the BIOS setup you have an
option to select whether you have an "ACPI OS" (wording of course
varies). I've never checked whether this may e.g. reflect itself
in the handover state of the GSI 0 RTE.

In your testing patch, could you also log the PIC mask bytes?
There ought to be at least one unmasked; or wait - there actually
is a spurious interrupt there (right before IOMMU initialization):

(XEN) spurious 8259A interrupt: IRQ7.

Hence I wonder if there's not possibly a 2nd one once the IOMMU
has been set up.

Jan

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