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

To: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking
From: Alex Williamson <alex.williamson@xxxxxx>
Date: Tue, 9 Mar 2010 16:25:40 -0700
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>, "Cihula, Joseph" <joseph.cihula@xxxxxxxxx>, Weidong Han <weidong.han@xxxxxxxxx>, "linux@xxxxxxxxxxxxxx" <linux@xxxxxxxxxxxxxx>, "keir.fraser@xxxxxxxxxxxxx" <keir.fraser@xxxxxxxxxxxxx>
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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.  That means we have to
> fill in the scope path with something, even if there's no device visible
> there.  We 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.

>  IMHO, 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.


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