Linux 5.18 Re-Enables Intel ENQCMD Usage In Time For Sapphire Rapids

Going back to 2019 the open-source ecosystem has been working on ENQCMD/ENQCMDS support for introduction with Xeon Scalable "Sapphire Rapids" as part of the Data Streaming Accelerator work. ENQCMD support was added to the Linux kernel but last June was outright disabled for being "broken beyond repair". It's now managed to be repaired and for Linux 5.18 this instruction usage is being re-enabled.

That earlier ENQCMD code within the Linux kernel was deemed to be in bad shape from a technical perspective. Intel's stellar and large open-source team sprung into action and began improving the code for this ENQCMD(S) handling for atomically submitting a work descriptor to a device.

They've been getting the new code into shape and last month I wrote how it looked like it was ready to be re-enabled. Indeed it has and that revised code has now been merged into Linux Git for the v5.18 kernel.

The code was merged to re-enable ENQCMD as part of improving the PASID (Process Address Space ID) code.

Linux 5.18 stable in turn should debut around the end of May, still likely ahead of the point of Intel ramping up Xeon Sapphire Rapids production. So the timing should ultimately work out fine thanks to Intel's timely enablement in the first place of this code (as well as Sapphire Rapids being pushed back from 2021) that there was sufficient time to iterate off the original enablement code.