Rocky Linux 9.2 for PowerPC (ppc64le) is now available

After additional testing and thorough investigation into the architecture-specific bug we discovered, the Rocky Linux team is pleased to announce the availability of Rocky 9.2 for the PowerPC (LE) or ppc64le architecture. Before upgrading your ppc64le machine to Rocky 9.2, review the section below on upgrading.

Our investigation has revealed that the environments under which our tests were performed were running a "pre-production" revision to the Power 9 CPU architecture, leading to segmentation faults we are able to reproduce both in emulated and physical environments with affected processor revisions (steppings). For a more detailed explanation, please read below.

Additional Technical Details

The PowerPC POWER 9 architecture has had multiple revisions to the physical CPU prior to being "Generally Available". Namely, the Design Document version 2.2 for Power 9 ISA (Power 9 DD2.2) was the first revision of the processor which Red Hat considers to be production ready, and thus supportable from a software perspective. In fact, there are many issues with both the 2.0 and 2.1 Design Document specifications which are at this time quite old.

During our investigation and collaboration with Red Hat on this issue, we discovered that on some of our testing machines, we were unable to reproduce the issue directly on the virtual machines, and upon inspection we discovered that the unaffected machines were all using version 2.2 or 2.3 of the POWER 9 specification. These VMs are ones which we use to perform native package and image builds, and are KVM guests provided to us via the Oregon State University Open Source Lab.

For our image builds, we utilize our Empanadas toolkit which uses ImageFactory and Oz to orchestrate image production inside qemu. Due to the nested nature of the ppc64le virtualization environment for building images, we must use qemu without KVM acceleration and rely on the emulation provided by QEMU--this is not ideal for a number of reasons. Firstly, it is slow, and takes a lot of time to iterate and test changes to see if they will resolve issues. Secondly, due to this bug, we have discovered a deficiency in QEMU in that it is only able to emulate the POWER 9 DD2.0 specification. Due to this, qemu is currently an unreliable test platform for us to conduct our testing and image building.

In order to resolve these issues, we are working both with QEMU upstream to investigate emulating the POWER 9 DD2.2 (and higher) steppings in QEMU, as well as to build our container and cloud images for ppc64le in an alternative fashion such that they can be released.

The team is thankful for your patience and consideration as we have worked to identify, scope, and resolve these issues while ensuring that the release as a whole is nominally safe for most users to upgrade to if they are using the ppc64le architecture. Regardless of the upstream bug status, the Rocky Linux team does consider this a regression between 9.0, 9.1, and 9.2, as we are able to reliably reproduce the failure in 9.2, as well as very occasionally under 9.1. The failure has not been experienced under 9.0 to date, though extensive testing has not been performed.

Upgrading

Before upgrading to Rocky Linux 9.2 on the ppc64le architecture, inspect the contents of /proc/cpuinfo on your physical and virtual machines. Some early models of POWER 9 processors are "pre production" silicon and are possibly vulnerable to many bugs preventing the stable usage of the system. There is no way to patch these issues in microcode as they are physical revisions to the CPU die to resolve these flaws.

If the below command returns a revision greater than or equal to 2.2, your system is supported. If it reports version 2.0 or 2.1, you will experience faults due to the regression in support for processor revisions.

$ grep -i revision /proc/cpuinfo
revision    : 2.3 (pvr 004e 1203)

In virtualized environments, your hypervisor host may be able to be configured to present the proper revision to the guest using libvirt, but if a physical system reports a POWER 9 Design Document revision below version 2.2, the only mitigation is to replace the CPU itself with one having a newer revision of the CPU steppings for POWER 9.

We are thankful for the upstream development work in Fedora Linux, the curation efforts in CentOS Stream, and the countless developers and projects from which these distributions are built.