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

[Alex Williamson <alex.williamson@xxxxxx>]

On Fri, Jan 22, 2010 at 1:47 AM, Weidong Han <weidong.han@xxxxxxxxx> wrote:
> I implemented a patch and attached.
>
> patch description:
> Â 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. ÂPls note that we
> don't know the devices under the "Include_all" DRHD are existent or not,
> because the scope of "Include_all" DRHD Âwon'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?
Thanks,

Alex

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