Linux 6.5 On AArch64 Sees New Extensions, KPTI Cleanup

The ARM64 (AArch64) architecture code has seen some clean-ups and support for new Arm ISA features with the in-development Linux 6.5 kernel.

Armv8.9 introduced the new Permission Indirection Extensions and that initial feature is enabled for Linux 6.5. Still to be built up in a future kernel release though is the Guarded Control Stacks and Permissions Overlays functionality. The Permission Indirection Extensions allow for a way to set permissions that more efficiently use the Translation Table Descriptors and allow for new permission types. The Permission Overlays allow for permissions to be progressively restricted by processes running at EL0 while reducing the number of calls to processes running at more privileged exception levels. Permission Overlays also allow avoiding costly TLB operations. Ultimately the Arm extensions allow for better managing of permissions around memory pages.

Also new to the 64-bit Arm code in Linux 6.5 is adding user-space support for Armv8.8 memcpy and memset instructions.

Plus this ARM64 pull has various Arm PMU updates, fixes, cleaning up of the Kernel Page Table Isolation (KPTI) code, and other maintenance updates. More details on the ARM64 updates for Linux 6.5 via this pull.