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

[Weidong Han <weidong.han@xxxxxxxxx>]

Alex Williamson wrote:
> 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,
>   
Currently multiple PCI segments are not supported in Xen yet. So you 
encounter issue on multiple PCI segment system. We will support it after 
xen 4.0.
Regards,
Weidong
> Alex
>
>   

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