[RFC][PATCH 00/17] Fix up the recent SRSO patches

[Peter Zijlstra]

Since I wasn't invited to the party (even though I did retbleed), I get to
clean things up afterwards :/

Anyway, this here overhauls the SRSO patches in a big way.

I claim that AMD retbleed (also called Speculative-Type-Confusion -- not to be
confused with Intel retbleed, which is an entirely different bug) is
fundamentally the same as this SRSO -- which is also caused by STC. And the
mitigations are so similar they should all be controlled from a single spot and
not conflated like they are now.

As such, at the end of the ride the new kernel command line and srso sysfs
files are no more and all we're left with is a few extra retbleed options.

Aside of that; this deals with a few implementation issues -- but not all known
issues. Josh and Andrew are telling me there's a problem when running inside
virt due to how this checks the microcode. I'm hoping either of those two gents
will add a patch to address this.