Intel's FRED Getting Ready To Meet The Linux Kernel

Since last year Intel Linux engineers have been busy working on FRED support for the Flexible Return and Event Delivery specification that will be found with future-generation processors. FRED overhauls how CPU transitions are handled between privilege levels and a design goal of lowering transition latencies and allow for more robust software use-cases.

Out this week is the ninth iteration of the Intel FRED patches for the Linux kernel. The FRED v9 patches bring many changes but at this pace it's looking like sooner rather than later these patches could be mainlined. Intel engineers continue testing the FRED Linux code on a CPU simulator with not yet having any pre-production hardware in their labs that actually has FRED support.

The principal goals of the Intel FRED architecture remain:

1) Improve overall performance and response time by replacing event delivery through the interrupt descriptor table (IDT event delivery) and event return by the IRET instruction with lower latency transitions.

2) Improve software robustness by ensuring that event delivery establishes the full supervisor context and that event return establishes the full user context.

The Linux kernel enablement is currently at 36 patches.

As always, it's great to see Intel's early work on upstreaming new CPU feature patches into the Linux kernel with these patches hopefully getting all tidied up well ahead of this functionality being found in released Intel processors. Released a few days ago was GNU Binutils 2.41 and that has the Intel LKGS / FRED support in place from the GNU Assembler perspective. Linux 6.3 also mainlined the Intel LKGS bits for "Load Kernel GS" as part of the FRED architecture.