Re: [Xen-devel] [PATCH] AMD/IOMMU: revert "amd/iommu: assign iommu devices to Xen"

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.06.19 at 10:48, <roger.pau@xxxxxxxxxx> wrote:
> On Mon, Jun 03, 2019 at 07:00:25AM -0600, Jan Beulich wrote:
>> This reverts commit b6bd02b7a877f9fac2de69e64d8245d56f92ab25. The change
>> was redundant with amd_iommu_detect_one_acpi() already calling
>> pci_ro_device().
>> 
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> I think this needs to be squashed together with your `AMD/IOMMU: don't
> "add" IOMMUs` patch, or else PVH dom0 will break because
> update_paging_mode will find devices not behind an IOMMU assigned to
> dom0, thus returning an error and crashing dom0.

How would update_paging_mode() get to see an IOMMU assigned
to Dom0? pci_ro_device() hands it to dom_xen. The point the other
patch you name is about is the fact that
_setup_hwdom_pci_devices() temporarily overrides the assignment
(I'm not convinced this is a good idea in general, but it surely is
needed for e.g. the graphics device that we may also hide) -
otherwise we could simply make amd_iommu_add_device() skip
dom_xen-assigned devices.

Jan



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