Xen 4.3/AMD: setup ssss:bb:dd.f for d0 failed (-ENODEV)

[Stefan Bader <stefan.bader@canonical.com>]

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While testing Xen 4.3 on my AMD testbox I noticed the following output from the
hypervisor (this has no visible effect on at least simple operation):

(XEN) setup 0000:00:18.0 for d0 failed (-19)
(XEN) setup 0000:00:18.1 for d0 failed (-19)
(XEN) setup 0000:00:18.2 for d0 failed (-19)
(XEN) setup 0000:00:18.3 for d0 failed (-19)
(XEN) setup 0000:00:18.4 for d0 failed (-19)
(XEN) setup 0000:00:19.0 for d0 failed (-19)
(XEN) setup 0000:00:19.1 for d0 failed (-19)
(XEN) setup 0000:00:19.2 for d0 failed (-19)
(XEN) setup 0000:00:19.3 for d0 failed (-19)
(XEN) setup 0000:00:19.4 for d0 failed (-19)

The PCI devices related to the output are all PCI host bridges:

00:18.0 Host bridge: Advanced Micro Devices, Inc. [AMD]
 Family 10h Processor HyperTransport Configuration
00:18.1 Host bridge: Advanced Micro Devices, Inc. [AMD]
 Family 10h Processor Address Map
00:18.2 Host bridge: Advanced Micro Devices, Inc. [AMD]
 Family 10h Processor DRAM Controller
00:18.3 Host bridge: Advanced Micro Devices, Inc. [AMD]
 Family 10h Processor Miscellaneous Control
00:18.4 Host bridge: Advanced Micro Devices, Inc. [AMD]
 Family 10h Processor Link Control
00:19.0 Host bridge: Advanced Micro Devices, Inc. [AMD]
 Family 10h Processor HyperTransport Configuration
00:19.1 Host bridge: Advanced Micro Devices, Inc. [AMD]
 Family 10h Processor Address Map
00:19.2 Host bridge: Advanced Micro Devices, Inc. [AMD]
 Family 10h Processor DRAM Controller
00:19.3 Host bridge: Advanced Micro Devices, Inc. [AMD]
 Family 10h Processor Miscellaneous Control
00:19.4 Host bridge: Advanced Micro Devices, Inc. [AMD]
 Family 10h Processor Link Control

This all seems to be related to PCI passthrough setup started from
xen/drivers/passthrough/vtd/iommu.c:intel_iommu_dom0_init() or
xen/drivers/passthrough/amd/pci_amd_iommu.c:amd_iommu_dom0_init()

While the Intel code skips over bridge type entries, the AMD code has no such
exception and will fail the handler with -ENODEV when find_iommu_for_device
fails. But I am not sure one can just compare implementations here.

Would someone have more insight to decide whether skipping host bridges in
amd_iommu_setup_dom0_device would make sense? I do not see any bad effects
caused by this but it does not look good and did not happen before.

-Stefan


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