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

To: Alex Williamson <alex.williamson@xxxxxx>
Subject: Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking
From: Weidong Han <weidong.han@xxxxxxxxx>
Date: Wed, 10 Mar 2010 11:28:15 +0800
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Noboru Iwamatsu <n_iwamatsu@xxxxxxxxxxxxxx>, "Cihula, Joseph" <joseph.cihula@xxxxxxxxx>, "Kay, Allen M" <allen.m.kay@xxxxxxxxx>, "linux@xxxxxxxxxxxxxx" <linux@xxxxxxxxxxxxxx>, "keir.fraser@xxxxxxxxxxxxx" <keir.fraser@xxxxxxxxxxxxx>
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Alex Williamson wrote:
On Wed, 2010-03-10 at 10:40 +0800, Weidong Han wrote:
Alex Williamson wrote:
I have a system with what I consider to be a valid DRHD that's getting
tripped up on this patch.  The problem is that the DRHD includes an
IOAPIC scope, where the IOAPIC is not materialized on the PCI bus.  I
think Xen is being overzealous in it's validity checking and that this
is a valid configuration.  What do others think?  Are IOAPICs a
special case that we can allow to be non-existent on the PCI bus?
Yes, IOAPIC can be not pci-discoverable. IOAPICs are only reported in the "Include_all" DRHD, and our patch won't check if the device is pci-discoverable or not for the "Include_all" DRHD. So I think the patch is no problem unless IOAPIC is not included in the "Include_all" DRHD. Can you post your boot logs?


That's a very subtle restriction, and I'm not sure how it works in
practice.  If I have a multi-IOH system, each with VT-d hardware, each
supporting interrupt remapping, each with one or more IOAPICs below
them, how can interrupt remapping work if we can only associate an
IOAPIC with the "include all" DRHD?  I'm confused.  Thanks,
Each IOH will have one "include all" DRHD which reports IOAPICs for each IOH.


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