ARM64 With Linux 5.20 Improves Its Meltdown Mitigation KPTI Code

The 64-bit Arm (ARM64) architecture updates have already been sent in for Linux 5.20 ahead of the merge window formally opening.

Notable this cycle when it comes to the 64-bit Arm architecture code (ARM64 / AArch64) includes a "major rework" to its Kernel Page Table Isolation (KPTI) code that is used for mitigating the Meltdown mitigation on relevant Arm CPU cores. The major rework to the ARM64 KPTI code is described as "makes it both more maintainable and considerably faster in the cases where it is required...so that the MMU remains enabled and the boot time is no longer slowed to a crawl for systems which require the late remapping."

KPTI is used for mitigating the Meltdown vulnerability on relevant CPUs.

Other ARM64 changes for Linux 5.20 include adding some new CPU errata for newer Arm implementations, handling of machine check errors more gracefully, support for direct swapping of the 2MiB transparent huge-pages on systems without MTE, improvements to the layout of vDSO objects, support for optionally disabling SVE and SME extensions via the kernel command-line, and other clean-ups/improvements.

The full list of ARM64 feature changes destined for Linux 5.20 via this pull request now awaiting action by Linus Torvalds following the Linux 5.19 stable release tomorrow.