RFC Fix file lock cache accounting, again

This is an attempt to fix file lock cache accounting (again). The bug was originally reported 2+ years ago [1] but was quickly reverted [2] for performance reasons.

A few years ago some ideas [3] were floated about how to improve the performance. Did any of those ever get implemented?

Testing shows "mm: improve performance of accounted kernel memory allocations" [4] helping some. But even with those patches, much of the original performance regression still remains, at least according to microbenchmarks.

Despite that regression, this being a security and correctness issue, it really needs to be fixed by default. Those who want to live on the edge (or have trusted user space) can disable it.

Patch 1 enables the fix by default, but allows disabling it at boot time.

Patch 2 allows disabling it at build time.

Patches 3 and 4 allow disabling it (along with all the CPU mitigations) using mitigations=off.

[1] 0f12156dff28 ("memcg: enable accounting for file lock caches")
[2] 3754707bcc3e ("Revert "memcg: enable accounting for file lock caches"")
[3] https://lore.kernel.org/lkml/[email protected]/
[4] https://lore.kernel.org/lkml/[email protected]/

Josh Poimboeuf (4):
fs/locks: Fix file lock cache accounting, again fs/locks: Add CONFIG_FLOCK_ACCOUNTING
mitigations: Expand 'mitigations=off' to include optional software
mitigations
mitigations: Add flock cache accounting to 'mitigations=off'

 .../admin-guide/kernel-parameters.txt         | 48 ++++++++++++++----
 arch/arm64/kernel/cpufeature.c                |  2 +-
 arch/arm64/kernel/proton-pack.c               |  6 +--
 arch/powerpc/kernel/security.c                | 14 +++---
 arch/s390/kernel/nospec-branch.c              |  2 +-
 arch/x86/kernel/cpu/bugs.c                    | 35 ++++++-------
 arch/x86/kvm/mmu/mmu.c                        |  2 +-
 arch/x86/mm/pti.c                             |  3 +-
 fs/Kconfig                                    | 15 ++++++
 fs/locks.c                                    | 31 +++++++++++-
 include/linux/bpf.h                           |  5 +-
 include/linux/cpu.h                           |  3 --
 include/linux/mitigations.h                   |  4 ++
 kernel/Makefile                               |  3 +-
 kernel/cpu.c                                  | 43 ----------------
 kernel/mitigations.c                          | 50 +++++++++++++++++++
 16 files changed, 174 insertions(+), 92 deletions(-)
 create mode 100644 include/linux/mitigations.h
 create mode 100644 kernel/mitigations.c

2.43.0