Linux 4.18 To Ship ARM64 SSBD For Spectre V4 Mitigation, LSE Atomics By Default

Since the unveiling of Spectre Variant Four last month ARM has been publishing patches for their mitigation for the 64-bit ARM CPUs. While the Intel/AMD and POWER mitigation landed for Linux 4.17, the SSBD work on AArch64 is landing for Linux 4.18.

ARM has put their Speculative Store Bypass Disable patches through several rounds of review and the code is now queued in for-next/core of new material slated to land in the Linux 4.18 merge window. The ARM64 SSBD patches are not currently marked for back-porting to existing stable series.

Those not wanting to incur the performance cost of SSBD can boot their system with ssbd=force-off.

Another ARM64 architectural change for Linux 4.18 is that LSE (Large System Extensions) Atomics are being enabled by default which use the LSE instructions for in-kernel atomic routines. The atomic instructions are designed to scale in "very large systems."