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

[Stefan Bader]

On 15.10.21 12:54, Kleber Sacilotto de Souza wrote:
> 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(-)
> 
Acked-by: Stefan Bader <stefan.bader at canonical.com>

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