[PATCH] mm: kfence: export kfence_enabled as global variables

[Alexander Potapenko]

> >
> > What is the problem you have encountered? Is the page-granular direct
> > map causing issues?
> We're working on a low memory target, page-granular mapping costed more
> (2M per 1GB) memory. Due to GKI constraints, it is not easy to disable
> CONFIG_KFENCE. So my intention was to move the judgement to runtime
> configurable w/ CONFIG_KFENCE on...
>
> Do you have any further suggestion/proposal on this? Many Thanks!

Right now CONFIG_KFENCE allocates 512Kb for the GKI kernel (only 63
objects instead of the default 255):
https://cs.android.com/android/kernel/superproject/+/common-android-mainline:common/arch/arm64/configs/gki_defconfig;l=686?q=CONFIG_KFENCE_NUM_OBJECTS
Where do 2M come from?