[PATCH RFC v2 0/1] x86: don't enable deprecated ISA extensions by default

[Jan Beulich]

IMO it has been a mistake from the beginning that all ISA extensions are
enabled by default. This way possible flaws e.g. in the compiler simply
go unnoticed. But that ship has sailed. However, for extensions where
support was removed from the compiler, we should at least consider whether
to disable them by default. That's what this series proposes (but see a
timing related RFC remark in patch 2).

Beyond that there are further discontinued extensions, which however gcc
still supports: HLE, VP2INTERSECT, and KeyLocker on the Intel side, TBM,
XOP, FMA4, and LWP for AMD. Question is what (if anything) to do there,
which may depend on what gcc's plans are.

Main question to be answered is when an appropriate time is to make such
adjustments (here as well as for the above items, if and when support
for them gets removed from gcc).

1: default to not accepting Xeon Phi insns

Jan