** Summary changed:

- xenial guest on arm64 drops to busybux under openstack bionic-rocky
+ xenial guest on arm64 drops to busybox under openstack bionic-rocky

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https://bugs.launchpad.net/bugs/1797092

Title:
  xenial guest on arm64 drops to busybox under openstack bionic-rocky

Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Xenial:
  Triaged
Status in linux source package in Bionic:
  Fix Released

Bug description:
  [Impact]
  on openstack rocky-bionic (with patch, see 1771662), xenial guests will fail 
to launch as they drop to the busybox prompt after booting. The reason is that 
the EFI firmware image switched to ACPI mode by default in bionic. We knew that 
was happening, and backported some minimal ACPI support to keep xenial guests 
booting (bug 1744754). But, now we're seeing guests panic when trying to 
initialize PCI.

  [Test Case]
  Deploy rocky-bionic OpenStack and try to launch a xenial guest.

  [Fix]
  Backport ACPI/PCIe support for arm64 from upstream.

  [ Regression Risk ]
  TLDR: Definitely warrants some regression testing on armhf/arm64, but 
regression risk seems low for other architectures. Here's a patch-by-patch risk 
analysis:

  > 0001-UBUNTU-Config-CONFIG_PCI_ECAM-y.patch
  Enables code that will be added in the next patch.

  > 0002-PCI-Provide-common-functions-for-ECAM-mapping.patch
  Only adds new code w/ no callers yet

  > 0003-PCI-generic-thunder-Use-generic-ECAM-API.patch
  As noted in the commit message:
  "The patch does not introduce any functional changes other than a very minor 
one: with the new code, on 64-bit platforms, we do just a single ioremap for 
the whole config space."

  > 0004-PCI-of-Move-PCI-I-O-space-management-to-PCI-core-cod.patch
  As noted, no functional change.

  > 0005-PCI-Move-ecam.h-to-linux-include-pci-ecam.h.patch
  As noted, no functional change.

  > 0006-PCI-Add-parent-device-field-to-ECAM-struct-pci_confi.patch
  This makes changes to the ecam code, but that was added in this series, so no 
regression risk there. The pci-thunder-pem changes will be regression tested on 
the hardware that uses that driver (Cavium ThunderX).

  > 0007-PCI-Add-pci_unmap_iospace-to-unmap-I-O-resources.patch
  Only adds new code, w/ no callers yet

  > 0008-PCI-ACPI-Support-I-O-resources-when-parsing-host-bri.patch
  Adds and calls a new function that is a no-op on !ARM (PCI_IOBASE is only 
defined on ARM). Also adds a call to pci_unmap_iospace(), which was added in a 
previous patch and is also a no-op on !ARM.

  > 0009-UBUNTU-Config-CONFIG_ACPI_MCFG-y.patch
  Enables code that will be added in the next patch.

  > 0010-PCI-ACPI-Add-generic-MCFG-table-handling.patch
  Adds parsing of a new ACPI table. A possible regression risk to platforms an 
MCFG table that were working fine w/ 4.4 and there's a latent bug in this 
parsing code.

  > 0011-PCI-Refactor-pci_bus_assign_domain_nr-for-CONFIG_PCI.patch
  As noted, no functional change intended.

  > 0012-PCI-Factor-DT-specific-pci_bus_find_domain_nr-code-o.patch
  Again, no functional change.

  > 0013-ARM64-PCI-Add-acpi_pci_bus_find_domain_nr.patch
  Only impacts ARM due to CONFIG_PCI_DOMAINS_GENERIC guard

  > 0014-ARM64-PCI-ACPI-support-for-legacy-IRQs-parsing-and-c.patch
  arm64-specific PCI initialization code - mitigate risk by regression testing 
on supported platforms (X-Gene, ThunderX).

  > 0015-ARM64-PCI-Support-ACPI-based-PCI-host-controller.patch
  Adds new code for arm64-ACPI support. We didn't previously support these 
devices, so regression risk is negligible.

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