If you happen to have a rare ARM64 platform with Simultaneous Multi-Threading (SMT) support, with the upcoming Linux 6.15 kernel there is set to finally be run-time SMT controls similar to the functionality long available on x86/x86_64 processors.
Since 2023 HiSilicon has been working on SMT run-time controls for ARM64 Linux to be able to offline sibling threads at run-time in situations where desired and to bring the SMT support back online as needed. The ARM64 SMT controls have been revised since that point and now finally in 2025 the support is set to be upstreamed.
Queued by way of the ARM64 Linux Git branch “for-next/core”, those ARM64 SMT control patches were queued up this past week — along with the renewed use of KPTI mitigations on some newer Arm processors.
The patches provide SMT run-time controls for both OF-based systems and ACPI-based systems. With Linux 6.15+ if running on an ARM64 processor that makes use of SMT, the /sys/devices/system/cpu/smt/control interface can be used for controlling the SMT state. Among the few ARM SoCs currently shipping with SMT is HiSilicon’s Kunpeng 930 and thus their motivation for getting this run-time control support into the mainline kernel.
