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

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?



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