Re: [PATCH v2 5/6] mm/slab: Support disabling KMALLOC_PARTITION_CACHES at boot

[Kees Cook <kees@kernel.org>]

On Fri, Nov 13, 2026 at 12:52:12AM -0800, Chris Down wrote:
> Kees Cook writes:
> > Swap the ifdef for a CONFIG-controlled static branch that defaults off
> > without CONFIG_KMALLOC_PARTITION_CACHES.
> 
> I've dropped the #ifdef in v3. kmalloc_partition_enabled now defaults to
> IS_ENABLED(CONFIG_KMALLOC_PARTITION_CACHES), and kmalloc_partition= is
> ignored without that option, so new_kmalloc_cache() doesn't need any
> #ifdef.
> 
> I've kept it as a bool rather than a static key, for the same reason as
> on 3/6: the only reader is new_kmalloc_cache(), at boot. When
> partitioning is off, kmalloc_type() still picks a partition index, but
> every one of them resolves to the normal cache. So the flag is never
> read on the allocation path.
> 
> The one place a static key would actually help is kmalloc_type(), where
> it could skip picking a partition and go straight to KMALLOC_NORMAL.
> Since kmalloc_type() is inline, that means exporting the key to modules.
> That seemed like more than this series needs, but if you think it's
> worth it I'm happy to add it.

I'll go look at v3. The goal was both immutability after init and
avoiding a branch in an allocation path.

-- 
Kees Cook