Intel Posts New Linux Patches Looking To Re-Enable ENQCMD Ahead Of Sapphire Rapids

While Intel is normally quite good with their new hardware support being in good shape well ahead of launch, their new code for supporting the ENQCMD functionality for the Data Streaming Accelerator (DSA) with Xeon "Sapphire Rapids" has been an exception. This summer the mainline Linux kernel disabled ENQCMD support since the code was "broken beyond repair" while now Intel engineers have sent out a new series looking to get it re-enabled.

The ENQCMD instruction (and ENQCMDS) allows atomically submitting a work descriptor to a device and part of the Data Streaming Accelerator debuting as part of next year's Sapphire Rapids processors. But the initial Linux kernel support code was in poor shape -- including insufficient protection against FPU state modification -- and led to it being disabled upstream. Intel originally upstreamed the ENQCMD work since last year.

With this set of patches, ENQCMD is looking to be re-enabled. We'll see though if the upstream kernel maintainers are happy now with the state of the code or further alterations will be required. If all goes well, the re-enabling could come for Linux 5.16 later this year -- still ahead of Sapphire Rapid's ramp in Q2.

While much of the Xeon Sapphire Rapids enablement for Linux has been completed for a while now, two other important pieces still settling down ahead of the next-gen Xeon Scalable is the Advanced Matrix Extensions (AMX) kernel-side support and x86 User Interrupts.