[SRU][R][PATCH 0/4] Take Intel platform into account for old microcode checks

[Michael Reed]

From: Michael Reed <Michael.Reed at canonical.com>

SRU Justification

[ Impact ]

The issue is Intel added code to Linux to check for old microcode. They base it on some processor fields not realizing there are multiple processor SKUs with the same processor field information. The result is the Linux wrongly prints out "Running old microcode" and sets taint bit 2 for some processor SKUs.
It takes specific Intel processor SKUs to hit the issue. This has been seen with Sapphire Rapids and Granite Rapids processors

[ Fix ]

These patches fix the issue

238be4ba x86/microcode: Refactor platform ID enumeration into a helper
d8630b67 x86/cpu: Add platform ID to CPU info structure
fab0c75d x86/cpu: Add platform ID to CPU matching structure
7989c393 x86/microcode: Add platform mask to Intel microcode "old" list

The patches fix false-positive "old microcode"/taint-bit-2 reports on Sapphire Rapids and Granite Rapids SKUs.



[ Test Plan ]
After booting the system check the /proc/sys/kernel/tainted file for the incorrect microcode error

 Without the fix:

  root at gnh-204:~# cat /proc/sys/kernel/tainted
  4
  root at gnh-204:~# dmesg | grep microcode
  [ 0.000000] x86/CPU: Running old microcode
  [ 10.088285] microcode: Enabled staging feature.
  [ 10.092931] microcode: Current revision: 0x01000434

 With the fix:

  root at gnh-204:~# cat /proc/sys/kernel/tainted
  0
  root at gnh-204:~# dmesg | grep microcode
  [ 10.090836] microcode: Enabled staging feature.
  [ 10.095475] microcode: Current revision: 0x01000434

[ Where problems could occur ]

The regression risk is low. This code is only touching the x86 microcode/CPU-matching code path and no other subsystems are affected.

[ Other Info ]

https://code.launchpad.net/~mreed8855/ubuntu/+source/linux/+git/resolute/+ref/kernel_taint_lp_2161748_intel

Dave Hansen (4):
  x86/microcode: Refactor platform ID enumeration into a helper
  x86/cpu: Add platform ID to CPU info structure
  x86/cpu: Add platform ID to CPU matching structure
  x86/microcode: Add platform mask to Intel microcode "old" list

 arch/x86/include/asm/microcode.h              |   2 +
 arch/x86/include/asm/processor.h              |   5 +
 arch/x86/kernel/cpu/intel.c                   |   1 +
 arch/x86/kernel/cpu/match.c                   |   3 +
 .../kernel/cpu/microcode/intel-ucode-defs.h   | 398 +++++++++++-------
 arch/x86/kernel/cpu/microcode/intel.c         |  54 ++-
 include/linux/mod_devicetable.h               |   2 +
 7 files changed, 294 insertions(+), 171 deletions(-)

-- 
2.53.0