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

[Alex Williamson <alex.williamson@xxxxxx>]

On Tue, Mar 9, 2010 at 4:25 PM, Alex Williamson <alex.williamson@xxxxxx> wrote:
> 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.

Not to beat a dead horse, but I believe my platform is exactly
following sections 8.3.1.1 of the VT-d spec for non-PCI discoverable
IOAPICs with a 2 byte path field.  This really needs to be fixed or
removed before Xen 4.0.0.  Thanks,

Alex

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