Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking

[Alex Williamson <alex.williamson@xxxxxx>]

On Tue, Mar 9, 2010 at 4:05 PM, Alex Williamson <alex.williamson@xxxxxx> wrote:
>
> In my case ir_ioapic_num will match nr_ioapics, so this shouldn't
> disable on my system.
>
> The problem with the current Xen code is that there's no requirement
> that an IOAPIC is a PCI device, yet we have to describe it as a device
> scope under a DRHD to enable interrupt remapping. ÂThat means we have to
> fill in the scope path with something, even if there's no device visible
> there. ÂWe happen to use the path of the IOAPIC if it were exposed so we
> can keep straight what it is, but nothing requires it to be enumerable
> on the PCI bus.

I guess we probably do need to use the actual IOAPIC PCI source ID so
we can enable source ID checking in the interrupt remapping table, but
I still don't think that implies it needs to be visible on a bus walk.

> ÂIMHO, the only important field in an IOAPIC DRHD scope
> is the enumeration ID, which allows the OS/VMM to map the IOAPIC to one
> defined in the MADT.

So actually, I might make the argument that the purpose of IOAPIC scope is:
1) Map an MADT defined APIC ID under a DRHD
2) Provide the source ID for the IOAPIC

Using the source ID to verify the IOAPIC exists isn't valid, though I
think it would be valid to verify the APIC ID against the MADT.
Thanks,

Alex

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