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

[Weidong Han <weidong.han@xxxxxxxxx>]

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.
Regards,
Weidong
> Alex
>
>   

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