[SRU][Bionic][PATCH 0/2] Revert PCI/MSI changes to fix boot issues (LP#1946149)

[Kleber Sacilotto de Souza]

BugLink: https://bugs.launchpad.net/bugs/194614

[ Impact ]
The bionic 4.15 kernels are failing to boot on r5.metal instances on AWS. The
default kernel is bionic/linux-aws-5.4(5.4.0-1056-aws), when changing to
bionic/linux-aws(4.15.0-1113-aws) or bionic/linux (4.15.0-160.168) the machine
fails to boot the 4.15 kernel.

This problem only appears on metal instances, which uses NVME instead of XVDA
devices.

[ Fix ]
It was discovered that after reverting the following two commits from upstream
stable the 4.15 kernels can be booted again on the affected AWS metal instance:

PCI/MSI: Enforce that MSI-X table entry is masked for update
PCI/MSI: Enforce MSI[X] entry updates to be visible

[ Test Case ]
Deploy a r5.metal instance on AWS with a bionic image, which should boot
initially with bionic/linux-aws-5.4. Install bionic/linux or bionic/linux-aws
(4.15 based) and reboot the system.

[ Where problems could occur ]
These two commits are part of a larger patchset fixing PCI/MSI issues which were
backported to some upstream stable releases. By reverting only part of the set
we might end up with MSI issues that were not present before the whole set was
applied. Regression potential can be minimized by testing the kernels with these
two reverted patches on all the platforms available.

Kleber Sacilotto de Souza (2):
  UBUNTU: SAUCE: Revert "PCI/MSI: Enforce MSI[X] entry updates to be
    visible"
  UBUNTU: SAUCE: Revert "PCI/MSI: Enforce that MSI-X table entry is
    masked for update"

 drivers/pci/msi.c | 20 --------------------
 1 file changed, 20 deletions(-)

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