ARM64 Prepping ARM v8.4 Features, KPTI Improvements For Linux 4.17

With the Linux 4.16 kernel release likely to happen this coming Sunday and that marking the opening of the Linux 4.17 merge window, many subsystem maintainers are preparing their "-next" trees of feature updates.

On the ARM64 architecture front (64-bit ARM / AArch64) there are more improvements as usual building with Linux continuing to dominate across the 64-bit ARM landscape.

Linux 4.17 will add support for more ARM v8.4 features including data independent timing (DIT) of instructions, unaligned atomic instructions and single-copy atomicity of loads and stores, LPADR/STLR instructions, and flag manipulation instructions.

ARM v8.4 was ARM Holdings' "2017" update to the architecture. ARM v8.4 hardware should begin appearing this year and more information on that architecture refinement via the ARM blog.

The Linux 4.17 kernel will also have a lot of refinements to the ARM64 capabilities code. Of the capabilities reworking, one change that stands out is this KPTI behavior change for page table isolation on ARM64. This will now ensure that KPTI is enabled if any of the installed CPUs detect the need for KPTI, namely for helping out with systems containing a mix of ARM cores where some may not need this defense.

There are also other ARM64 updates as outlined here.

The ARM SoC branch is also beginning to fill up with the changes for Linux 4.17. On that front there is now support for the Qualcomm Centriq 2400 REP BMC, among other support improvements.