** Description changed:

  [Impact]
  After upgrading an Ubuntu/arm64 KVM host past xenial, your xenial-based 
guests will fail to boot.
  
  [Test Case]
  Boot a xenial cloud image with qemu-efi-aarch64 from artful/bionic.
  
  [Regression Risk]
  I've tested booting a xenial cloud image in bionic (ACPI mode), and 
regression tested w/ xenial's qemu-efi (DTB mode). I've regression tested on a 
Cavium ThunderX CRB1S, Caviumt ThunderX CRB2S and an APM X-Gene 2 Merlin board.
  
  Patches 1-5 change only code in the GICv3 driver. The xenial GA kernel
  only supported 2 GICv3 systems - the 1 socket and 2 socket variants of
  the Cavium ThunderX CRB - and I've regression tested on those systems.
  
  Patch 6 only adds new macro definitions.
  
  Patch 7 is restricted to devicetree code, except for a change to
  earlycon.c:param_setup_earlycon(). In the case that 'earlycon' is passed
  on the cmdline (vs. earlycon=something), this function used to return 0
  - but now it will return -ENODEV on non-devicetree systems, which is a
  subtle API change. However, according to kernel-parameters.txt (and the
  code itself), 'earlycon' by itself is only valid on devicetree systems.
  Just to be sure, I booted an x86 system up w/ 'earlycon' with and
  without this series, and observed no difference.
  
  Patch 8 adds the SPCR table parser, but no caller to it yet. It also
  modifies the same earlycon code as Patch 7 - here it avoids earlycon
  init in the case that the devicetree-specific 'earlycon' was passed. As
  mentioned in my analysis Patch 7, this codepath is only supported for
  devicetree systems, and has been regression tested on x86.
  
  Patch 9 turns on CONFIG_ACPI_SPCR_TABLE - however, this driver will only
  be built for arm64. TBH, I'm not 100% sure how Kconfig knows not to
  build this for other archs - but I checked the logs, and there's no
  spcr.o built on other archs. (Not that that should be a problem - they
  would just grow a bit of unused code).
  
  Patch 10 only touches arm64-specific code, adding the call to
- parse_spcr().
+ parse_spcr(), so risk is limited to arm64.
  
  Patch 11 adds a new match method to the ARM-specific pl011 console
- driver.
+ driver, so regression risk to other architectures is negligible.

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https://bugs.launchpad.net/bugs/1744754

Title:
  qemu-efi-aarch64 in >= artful can't boot xenial cloud images

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