On 2023/2/7 18:28, Alexander Potapenko wrote:
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?
Hi Alexander,
It is not from KFENCE cost itself, but from the requirement it needs
page-granular mapping.
2M per 1GB cost is from linear mapping for page granularity. You can see
can_set_direct_map() is used for whether allowing section mapping or not.
