[PATCH v3 0/6] mm/slab: Support selecting slab hardening features at boot

[Chris Down]

Slab hardening settings are currently all build time choices. This means
that, unfortunately, hosts with different requirements end up needing
separate kernel images. At Meta, for example, some hosts are built with
these options and the rest of the fleet isn't, and that's one of the
things that keeps those kernels apart.

This series does two things:

- SLAB_FREELIST_HARDENED and SLAB_FREELIST_RANDOM are cheap enough with
  sheaves that it makes more sense to just enable them by default than
  to make them switchable. With both on, system level benchmarks didn't
  change measurably, only slowpath heavy microbenchmarks did [1].

- SLAB_BUCKETS and KMALLOC_PARTITION_CACHES cost memory (Harry measured
  about 1 MiB and 18 MiB respectively after boot on a 64 CPU VM [2]), so
  they get slab_buckets= and kmalloc_partition= boot parameters, which
  default to on when the option is built in.

Whether those two should be folded into a single slab_hardening= is
still open [3].

v3:

- Rebase onto slab/for-next.
- Always build the slab_buckets and kmalloc_partition tests and skip them
  at runtime when the option isn't built in, instead of leaving them out
  with #ifdef (Kees).
- Declare slab_buckets_enabled and kmalloc_partition_enabled in
  mm/slab.h without any #if (Kees).
- Drop the remaining #ifdefs around slab_buckets= and
  kmalloc_partition=. Both are now always registered and ignored when
  the option isn't built in (Kees).
- Keep both flags as plain __ro_after_init bools rather than static
  keys, since they're only read when caches are created and not on the
  allocation path.

v2:

- Make SLAB_FREELIST_HARDENED and SLAB_FREELIST_RANDOM default y instead
  of adding boot parameters for them (Vlastimil).
- Skip the memdup_user() part of the slab_buckets test on !MMU
  (Sashiko).
- Keep slab_buckets= and kmalloc_partition= separate for now. We can
  discuss whether to merge them into slab_hardening= or similar, as
  Harry suggested.

v2: https://lore.kernel.org/r/cover.1793253633.git.chris@xxxxxxxxxxxxxx
v1: https://lore.kernel.org/r/cover.1793086056.git.chris@xxxxxxxxxxxxxx

[1] https://lore.kernel.org/r/auITixAJMfLtfa7i@xxxxxxxxxxxxxx
[2] https://lore.kernel.org/r/179312451613.474906.1475329637924619088@xxxxxxxxxx
[3] https://lore.kernel.org/r/aud4gPOUzvHtLYnJ@thinkstation

Chris Down (6):
  mm/slab: Enable SLAB_FREELIST_HARDENED by default
  mm/slab: Enable SLAB_FREELIST_RANDOM by default
  mm/slab: Support disabling SLAB_BUCKETS at boot
  slub_kunit: Add a test for the slab_buckets boot parameter
  mm/slab: Support disabling KMALLOC_PARTITION_CACHES at boot
  slub_kunit: Add a test for the kmalloc_partition boot parameter

 .../admin-guide/kernel-parameters.txt         | 15 ++++
 lib/tests/slub_kunit.c                        | 85 +++++++++++++++++++
 mm/Kconfig                                    | 11 +++
 mm/slab.h                                     |  3 +
 mm/slab_common.c                              | 52 ++++++++++--
 5 files changed, 157 insertions(+), 9 deletions(-)


base-commit: ce6518e61e3b4bf4f97f7ac6204049b9eba7eb75
-- 
2.56.1