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

[Stefan Bader]

On 18.10.18 08:14, Juerg Haefliger wrote:
> 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.

OK, maybe its better than I feared. It is just very hard to keep track of things
with other stuff going on in parallel. I just very vaguely remember that for
Bionic/4.15 and possibly later, IBRS/IBPB was only decided based on cpu features
while some of what we did there was an additional sysfs interface.

-Stefan
> 
> ...Juerg
> 


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