[SRU][X/aws][PATCH v2 0/1] aws: revert change to support instance types > 255 cpu cores

[Andrea Righi]

BugLink: https://bugs.launchpad.net/bugs/1918590

[Impact]

In LP: #1913739 we applied a fix to properly detect the right amount of
cores in AWS large instance types (> 255). However, this fix seems to
work properly only with kernels > 4.4. Even if it doesn't seem to
introduce any failure or regression, it is probably just safer to revert
this commit in the Xenial kernel, and keep it on the other kernels (> 4.4).

[Test plan]

Boot an instance type with > 255 cpus and check the amount of cores
detected.

[Fix]

Revert commit:

  561ef22a7d396289a1c5a1d18057ccdf9bb59826 ("iommu/vt-d: Gracefully handle DMAR units with no supported address widths")

[Regression potential]

Reverting the commit simply restores the old behavior, so we won't be
able to detect the right amount of CPUs in large instances, but we are
sure that we won't also introduce any potential failure or regressions
by restoring the previous behavior. And this is affecting only the
Xenial kernel, that is approaching to EOL.

ChangeLog (v1 -> v2):
  - create a new bug instead of re-using the old one when the original
    fix was applied