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

[Weidong Han <weidong.han@xxxxxxxxx>]

Alex Williamson wrote:
> On Fri, Jan 22, 2010 at 1:47 AM, Weidong Han <weidong.han@xxxxxxxxx> wrote:
>   
> > I implemented a patch and attached.
> >
> > patch description:
> >   In order to make Xen more defensive to VT-d related BIOS issue, this patch
> > ignores a DRHD if all devices under its scope are not pci discoverable, and
> > regards a DRHD as invalid and then disable whole VT-d if some devices under
> > its scope are not pci discoverable. But if iommu=force is set, it will
> > enable all DRHDs reported by BIOS, to avoid any security vulnerability with
> > malicious s/s re-enabling "supposed disabled" devices.  Pls note that we
> > don't know the devices under the "Include_all" DRHD are existent or not,
> > because the scope of "Include_all" DRHD  won't enumerate common pci device,
> > it only enumerates I/OxAPIC and HPET devices.
> >     
> Hi All,
>
> 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?
Regards,
Weidong
> Thanks,
>
> Alex
>   



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