Re: xen interrupt system

[Christoph Egger <Christoph_Egger%gmx.de@localhost>]

On Friday 21 August 2009 08:17:27 Christoph Egger wrote:
> On Thursday 20 August 2009 18:07:31 Manuel Bouyer wrote:
> > On Thu, Aug 20, 2009 at 05:53:45PM +0200, Christoph Egger wrote:
> > > > > Why are we doing this in first place ?
> > > > > Disabling ioapics doesn't really sound to be right.
> > > >
> > > > Because we don't know the state of the system. So we first
> > > > disable all interrupt pins, and then reenable the ones we use.
> > > > Maybe this could be skipped in the Xen case. It's probably worth a
> > > > try.
> > >
> > > I tried but this alone had no effect.
> > >
> > > During boot, I also have this in serial output:
> > > [...]
> > > svwsata0: ServerWorks HT-1000 SATA Controller (rev. 0x00)
> > > linkdev LNKS returned ACPI global irq 7, line 7
> > > (XEN) io_apic.c:2292:
> > > (XEN) ioapic_guest_write: apic=0, pin=7, old_irq=-1, new_irq=94
> > > (XEN) ioapic_guest_write: old_entry=00000948, new_entry=0000a95e
> > >
> > >
> > > (XEN) ioapic_guest_write: Installing bogus unmasked IO-APIC entry!
>
> There's a C comment right before this message:
>
> /* This pin leads nowhere but the guest has not masked it. */
>
> When we this message, then Xen didn't really allocate the interrupt for us
> since it does a more strict validation check if the irq we want to allocate
> is really an ioapic interrupt. irq 94 is not an existing ioapic interrupt
> on that machine.
>
> > > ioapic0: int7
> > > 0x1a95e<vector=0x5e,delmode=0x1,logical,actlo,level,masked,dest=0x0>
> > > 0xff000000<target=0xff>
> > > svwsata0: using ioapic0 pin 7, event channel 7 for native-PCI interrupt
> >
> > We had an active entry for this pin. I guess Xen wants us to mask it
> > before changing it (but a look in the sources would tell more), this is
> > what the code in ioapic_attach() tries to do (in fact, it reprograms
> > the apic from scratch).
> > The old entry was IOAPIC_REDLO_DSTMOD, IOAPIC_REDLO_DEL_LOPRI and we're
> > trying to add the IOAPIC_REDLO_ACTLO | IOAPIC_REDLO_LEVEL flags (in
> > addition to changing the vector). I don't know why Xen says it's invalid,
> > a look at the sources could give details about this.
>
> Xen's recent interrupt change happened to support per-cpu vectors. I
> suppose we need to change our way in allocating interrupts.

I'm in discussion with XenSource and Intel. They say, the way we initialize
ioapics is okay but Dom0 should not use vectors at all.

Christoph