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

To: Weidong Han <weidong.han@xxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] VT-d: improve RMRR validity checking
From: Alex Williamson <alex.williamson@xxxxxx>
Date: Tue, 09 Mar 2010 20:37:33 -0700
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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On Wed, 2010-03-10 at 11:28 +0800, Weidong Han wrote:
> 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?
> >>     
> >
> > Weidong,
> >
> > 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.

Wouldn't that imply multiple PCI segments?  The configuration I'm
looking at has multiple IOHs, all on the same PCI segment.  By my
reading of the spec, we're only allowed to declare INCLUDE_PCI_ALL for
one DRHD within the segment.  Am I incorrect?  Thanks,


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