---
- branch: MAIN
  date: Sat Dec 22 10:00:39 UTC 2018
  files:
  - new: '1.22'
    old: '1.21'
    path: src/sys/arch/x86/x86/spectre.c
    pathrev: src/sys/arch/x86/x86/spectre.c@1.22
    type: modified
  id: 20181222T100039Z.408fd66a4ba3f2c035ab2c4465d94e401f815024
  log: |
    In the end, disable the supposed architectural SpectreV2 mitigation on
    AMD f12h and f16h. The SDMs of these CPUs haven't been updated since, and
    we shouldn't assume the position of the bits, we just can't know where
    they are.

    Initially I included f12h and f16h because f10h is actually documented
    to have a bit to disable the indirect branch predictor, and there were
    patches available in SuSE and CentOS that were treating f10h/f12h/f16h
    all the same. Knowing that SuSE has ties with AMD, it seemed safe to
    assume that these patches were correct and that f12h and f16h could
    indeed be treated the same way as f10h.

    But these patches have now disappeared, and the main Linux branch
    doesn't have them, without clear explanation. Therefore, I prefer to
    roll-back.
  module: src
  subject: 'CVS commit: src/sys/arch/x86/x86'
  unixtime: '1545472839'
  user: maxv