[Patch v3 Part2 0/9] x86/microcode: Declare microcode safe for late loading

[Ashok Raj]

Hi Boris,

Here is v3 of part2. v1 Part2 is here[1]
These address feedback from Thomas here [2] posted as "Part2 v2[cleanup]"

Thanks Thomas for the feedback, and Tony for fixes to my commit logs adding
more clarity!

This series  should apply on top of tip/x86/microcode.

Please help with review and apply.

Patch 1-4:
	Cleanup patches that were in response to comments from
	Thomas[2].

Patch 5: Preparatory patch to keep warning and taint in same function.
Patch 6: Add minimum revision ID for Intel microcode
Patch 7: Add a generic mechanism to declare safe late loading.
Patch 8: Drop the unneeded wbinvd() after the minimum rev update
Patch 9: Optional - Allows testing with override minrev.

Tests Done:

1. For values other than 1 to reload file, will not report an error.
   For e.g. 

   echo 2 > reload
   bash: echo: write error: Invalid argument

2. In cases where there is no file OR no new update found, echo 1 will not
   report an error

   echo 1 > reload

3. When trying to load a file with minrev=0, there will be a log in dmesg
   and will also return -EINVAL in response to the write to "reload".

[105682.501898] microcode: Late loading denied: Microcode header does not specify a required min version

root@araj-ucode:/sys/devices/system/cpu/microcode# cat /proc/sys/kernel/tainted
0

4. Offline a primary CPU and attempt to load, must not taint the kernel.

# echo 0 > cpu2/online

[  378.725868] smpboot: CPU 2 is now offline

#echo 1 > /sys/devices/system/cpu/microcode/reload

[  388.024968] microcode: Not all CPUs online, aborting microcode update.

#cat /proc/sys/kernel/tainted
0
# echo 1 cpu2/online

[  398.664452] smpboot: Booting Node 0 Processor 2 APIC 0x4

5. When using the optional patch 9 to override minrev, kernel will be
   tainted.

root@araj-ucode:/sys/devices/system/cpu/microcode# cat /proc/sys/kernel/tainted
0
   echo Y > /sys/kernel/debug/microcode/override_minrev
   echo 1 > /sys/devices/system/cpu/microcode/reload

[  491.489986] microcode: Bypassing minrev enforcement via debugfs
[  491.649550] microcode: updated to revision 0x2b000070, date = 2022-08-22
[  493.595267] microcode: Reload succeeded, microcode revision: 0x2b000041 -> 0x2b000070
[  493.595360] microcode: Microcode late loading tainted the kernel

root@araj-ucode:/sys/devices/system/cpu/microcode# cat /proc/sys/kernel/tainted
4

[1] https://lore.kernel.org/lkml/20230113172920.113612-1-ashok.raj@xxxxxxxxx/
[2] https://lore.kernel.org/lkml/87y1pygiyf.ffs@tglx/

Cheers,
Ashok

Ashok Raj (9):
  x86/microcode: Taint kernel only if microcode loading was successful
  x86/microcode: Report invalid writes to reload sysfs file
  x86/microcode/intel: Fix collect_cpu_info() to reflect current
    microcode
  x86/microcode: Do not call apply_microcode() on sibling threads
  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   | 71 +++++++++++++++++++-------
 arch/x86/kernel/cpu/microcode/intel.c  | 71 +++++++++++++++++++++-----
 arch/x86/Kconfig                       |  7 +--
 5 files changed, 119 insertions(+), 37 deletions(-)


base-commit: a9a5cac225b0830d1879640e25231a37e537f0da
-- 
2.37.2

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>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Martin Pohlack <mpohlack@xxxxxxxxx>