[PATCH v1 Part2 0/5] Declare safe late loadable microcode

[Ashok Raj]

Hi Boris & Thomas,

Attached is a series that adds support for microcode to declare a minimum
revision number that is safe for late loading.

Late loading was disabled[1] in 5.19 due to lack of an ability to declare
when a microcode is safe for late loading. 

This series is inspired by recommendations from Thomas [2]. 

This series is part2 and applies on top of that cleanup series part1[3].

- Move where the warning and tainting is done to the same function. It
  helps when later patches enable late loading, to issue the warning only
  when the vendor doesn't support a mechanism for declaring a microcode
  for safe late loading.

- Add meta-data for Intel microcode to specify a minimum revision that the
  CPU must be on before attempting to load this microcode.

- Extend this as a generic mechanism to allow the common infrastructure to
  permit late loading.

- Some CPUs required a wbinvd() to be issued before attempting to load a
  microcode. These were later addressed via microcode patches. Now there
  exists a mechanism to declare a minimum revision, those flushes aren't
  required any longer.

- Provide a mechanism to override minrev as a way to bypass during the
  transition. It is recommended to always use early loading, especially if
  one is moving to a newer kernel. This is a chicken bit option :) and
  completely optional.

[1] https://lore.kernel.org/lkml/20220524185324.28395-3-bp@xxxxxxxxx/
[2] https://lore.kernel.org/linux-kernel/alpine.DEB.2.21.1909062237580.1902@xxxxxxxxxxxxxxxxxxxxxxx/
[3] https://lore.kernel.org/lkml/20230109153555.4986-1-ashok.raj@xxxxxxxxx/

Cheers,
Ashok

Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>
Cc: x86 <x86@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Tony Luck <tony.luck@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Alison Schofield <alison.schofield@xxxxxxxxx>
Cc: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Cc: Thomas Gleixner (Intel) <tglx@xxxxxxxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Cc: Stefan Talpalaru <stefantalpalaru@xxxxxxxxx>
Cc: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Rafael J. Wysocki <rafael@xxxxxxxxxx>
Cc: Peter Zilstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>


Ashok Raj (5):
  x86/microcode: Move late load warning to the same function that taints
    kernel
  x86/microcode/intel: Add minimum required revision to microcode header
  x86/microcode: Add a generic mechanism to declare support for minrev
  x86/microcode/intel: Drop wbinvd() from microcode loading
  x86/microcode: Provide an option to override minrev enforcement

 arch/x86/include/asm/microcode.h       |  4 ++
 arch/x86/include/asm/microcode_intel.h |  3 +-
 arch/x86/kernel/cpu/microcode/core.c   | 36 ++++++++++++++---
 arch/x86/kernel/cpu/microcode/intel.c  | 55 ++++++++++++++++++++------
 arch/x86/Kconfig                       |  7 ++--
 5 files changed, 83 insertions(+), 22 deletions(-)

-- 
2.34.1