[PATCH 0/5] arm64: errata: Expand speculative SSBS workaround

[Mark Rutland]

Hi,

A number of Arm Ltd CPUs suffer from errata whereby an MSR to the SSBS
special-purpose register does not affect subsequent speculative
instructions, permitting speculative store bypassing for a window of
time.

We recently addressed this for Cortex-X4 and Neoverse-V3:

  https://lore.kernel.org/linux-arm-kernel/20240508081400.235362-1-mark.rutland@arm.com/

... which was merged into mainline in v6.10-rc1.

Since then, Arm have published Software Developer Errata Notice (SDEN)
documents for a number of CPUs affected by the same issue. This series
updates the workaround to handle those CPUs.

Since there are now a number of CPUs known to be affected, I've merged the
Kconfig options to avoid duplicate text and boilerplate ifdeffery.

Largely this is mechanical work to add the IDs and handle them for
detection, but I have made two choices I'd like to check:

* For the common Kconfig symbol I've used CONFIG_ARM64_ERRATUM_3194386
  (matching the Neoverse-V3 erratum ID), following the example of
  CONFIG_ARM64_ERRATUM_1319367 which covers Cortex-A57 erratum 1319537
  and Cortex-A72 erratum 1319367.

  Given the precedent, I'm assuming that's fine. I also considered
  ARM64_ERRATUM_SPECULATIVE_SSBS, but that required reflowing the
  table in the documentation, which is very churny.

* I updated the runtime message to say:

    "SSBS not fully self-synchronizing",

  ... rather than listing every relevant erratum ID, as this would
  become very long:

    "ARM errata 3194386, 3312417, 3324334, 3324335, 3324336, 3324338, 3324339, 3456091"

  ... and if we end up needing to add more affected CPUs it would get
  even longer.

  I'm happy to use the latter if that's preferable.

Mark.

Mark Rutland (5):
  arm64: cputype: Add Cortex-X3 definitions
  arm64: cputype: Add Cortex-A720 definitions
  arm64: cputype: Add Cortex-X925 definitions
  arm64: errata: Unify speculative SSBS errata logic
  arm64: errata: Expand speculative SSBS workaround

 Documentation/arch/arm64/silicon-errata.rst | 16 ++++++++-
 arch/arm64/Kconfig                          | 36 +++++++--------------
 arch/arm64/include/asm/cpucaps.h            |  2 +-
 arch/arm64/include/asm/cputype.h            |  6 ++++
 arch/arm64/kernel/cpu_errata.c              | 17 ++++++----
 arch/arm64/kernel/proton-pack.c             |  2 +-
 6 files changed, 44 insertions(+), 35 deletions(-)

-- 
2.30.2