[SRU][Trusty][PULL] Cleanup Meltdown/Spectre implementation (LP: #1779848)

[Juerg Haefliger]

On Thu, 11 Oct 2018 09:49:33 +0200
Stefan Bader <stefan.bader at canonical.com> wrote:

> On 09.10.2018 15:37, Juerg Haefliger wrote:
> > BugLink: https://bugs.launchpad.net/bugs/1779848
> > 
> > == SRU Justification ==
> > 
> > Ubuntu kernels contain Meltdown and Spectre mitigations that are
> > largely based on embargoed patches but what eventually landed in
> > upstream is different in some places. We should clean up the
> > different kernels to bring them closer in line with upstream. 
> 
> The testing for this is as good as one can get. Just for clarity, I
> believe the main difference we had and possibly still have in some
> cases is the handling of IBRS/IBPB and how things are exposed as
> knobs to twiddle. How did you do those and (that might be for Tyler)
> do we have a somehow documented decision of the goal. I made some
> decision when working on Xenial and I fear those might be different
> than yours for the lack of guidance.

Sorry, your reply slipped through the cracks. I'm not sure what you
mean. AFAIK our specific runtime control knobs and boottime options
and their implementations are identical for Trusty and Xenial. I just
rearranged things to integrate it more logically with all the other
modifications but there should be no functional changes. These are the
last 2 commits in the PR. As for testing those changes, I just verified
that I can twiddle the knobs as before and that the kernel boots.

...Juerg
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