The purpose of this RFC is to supplement our discussion in LSF/MM-25.
This is sent as a proof of concept. It applies on top of v6.14-rc7.
With the goal of increasing security and improving CPU efficiency,
we would like to propose making KSM synchronous and partitioned.
The synchronous aspect eliminates the need of ksmd running in the
background. Instead, userspace can trigger merging on the specified
memory region synchronously. Contrary to SKSM [1], which uses
MADV_MERGE, we also propose sysfs and syscall based alternatives.
The partitioned aspect divides the merge space into security domains.
Merging of pages only takes place within a partition, improving security.
Furthermore, trees in each partitioning becomes smaller, improving CPU
efficiency.
Proposal 1: SYSFS Interface
KSM_SYSFS=/sys/kernel/mm/ksm
echo "part_1" > ${KSM_SYSFS}/ksm/control/add_partition
ls ${KSM_SYSFS}/part_1/
pages_scanned pages_to_scan sleep_millisecs ...
echo "pid start_addr end_addr" > ${KSM_SYSFS}/part_1/trigger_merge
Proposal 2: SYSCALL Interface
Partition can be created or opened using:
int ksm_fd = ksm_open(ksm_name, flag);
name specifies the ksm partition to be created or opened.
flags:
O_CREAT
Create the ksm partition object if it does not exist.
O_EXCL
If O_CREAT was also specified, and a shared memory object
with the given name already exists, return an error.
Trigger the merge using:
ksm_merge(ksm_fd, pid, start_addr, size);
[1] https://lore.kernel.org/linux-mm/20250228023043.83726-1-mathieu.desnoyers@xxxxxxxxxxxx/
Sourav Panda (6):
mm: introduce SELECTIVE_KSM KConfig
mm: make Selective KSM synchronous
mm: make Selective KSM partitioned
mm: create dedicated trees for SELECTIVE KSM partitions
mm: trigger unmerge and remove SELECTIVE KSM partition
mm: syscall alternative for SELECTIVE_KSM
arch/x86/entry/syscalls/syscall_64.tbl | 3 +-
include/linux/ksm.h | 4 +
mm/Kconfig | 11 +
mm/ksm.c | 823 ++++++++++++++++++++++---
4 files changed, 751 insertions(+), 90 deletions(-)
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2.49.0.395.g12beb8f557-goog
