Chapter 4. Important changes to external kernel parameters

indirect_target_selection=

[X86, Intel] Mitigation control for the Indirect Target Selection (ITS) issue on Intel CPUs. Updated microcode is required for the IBPB fix.

sdw_mclk_divider=

[SDW, Intel] Specify the MCLK divider for Intel SoundWire buses when the BIOS does not provide the clock rate properly.

thp_shmem=

[KNL, MM] Control the default huge page policy per size for the internal shmem mount.

transparent_hugepage_shmem=

[KNL, MM] Control the huge page allocation policy for the internal shmem mount.

tsa=

[X86, AMD] Control mitigation for Transient Scheduler Attacks on AMD CPUs.

init=

[KNL] Format: <full_path> Run the specified binary instead of /sbin/init as the system init process.

intremap=

[X86-64, Intel-IOMMU, EARLY]

kvm-arm.mode=

[KVM, ARM, EARLY] Select the Arm KVM virtualization mode.

kvm-arm.vgic_v3_group0_trap=

[KVM, ARM, EARLY] Trap guest accesses to GICv3 group‑0 registers to the host for stricter isolation and debugging.

libata.force=

[SATA/ATA] Per‑port options:

nohz

[KNL] Disable the tick when a single task runs, and offload other kernel work such as RCU callbacks. Equivalent to nohz_full. A residual 1 Hz tick is offloaded to workqueues; affine these to housekeeping CPUs via the global workqueue CPU mask. See also rcu_nocbs= and isolcpus=.

pci=

[PCI] ACS configuration example updated to include a device selector: pci=config_acs=10x@pci:0:0:: Configure supported devices to enable P2P Request Redirect, disable Translation Blocking, and leave Source Validation unchanged along the specified device path.

pcie=

[PCIE] New system‑wide flag: notph:: Disable PCIe TLP Processing Hints support when CONFIG_PCIE_TPH is enabled.

pcie_aspm=

[PCIE] Forcibly enable or ignore PCIe Active State Power Management. Behavior unchanged; use alongside pcie= flags where needed.

preempt=

[KNL, Scheduler] Preemption control modes. New: lazy:: Scheduler‑controlled mode similar to full. The task gets one HZ tick to yield before the scheduler forces preemption. A preemption is counted when the task returns to user space.

print-fatal-signals=

[KNL] Enable debugging output for fatal signals.

skew_tick=

[KNL, EARLY] Offset the periodic timer tick per CPU to reduce contention in large systems and with CONFIG_MAXSMP.

slub_debug=

[MM] SLUB allocator debugging; slub_nomerge remains a legacy alias. See Documentation/mm/slub.rst.

spectre_v2=

[X86] Selecting a specific mitigation does not force‑enable user‑space mitigations. Selecting on enables kernel protections and mitigates user‑to‑user task attacks. Selecting off disables both.

tsc=

[X86] Disable clocksource stability checks for TSC.

transparent_hugepage_shmem=

[KNL, MM] Values: always, within_size, advise, never, deny, force. Controls the internal shmem mount policy. See Documentation/admin-guide/mm/transhuge.rst.

mitigations=

[Multi‑arch] Selecting off disables a set of kernel and user‑space mitigations. The equivalence list now includes indirect_target_selection=off on X86, in addition to existing entries such as kpti=0 on Arm64, gather_data_sampling=off, kvm.nx_huge_pages=off, l1tf=off, mds=off, and related X86 flags.

timer_migration

When set to a non-zero value, the kernel attempts to migrate timers away from idle CPUs to help those CPUs remain in low-power states longer.