Linus Torvalds has just announced the release of Linux kernel 6.18-rc4, keeping the development cycle for the next major kernel version on its regular Sunday schedule. While today also saw the release of several stable kernel updates, this new release candidate gives us a clear look at what’s coming in the near future.
This week’s update is notable for including important fixes for upcoming and current-generation AMD hardware, as well as addressing a performance regression found in the power management code. Torvalds’s announcement (ki bi jo običajno našli na LKML – LINUX KERNEL MAILING LIST) indicates a relatively normal development week, with fixes spread across various subsystems.
Key Hardware Fixes in 6.18-rc4
The most significant changes in this release candidate are focused on the x86 architecture, particularly for AMD processors.
Fixing the AMD Zen 5 “RDSEED” Bug
One of the most critical patches included in 6.18-rc4 is a workaround for the recently discovered bug in AMD’s Zen 5 processors related to the RDSEED instruction. This instruction is crucial for generating high-quality random numbers.
The bug, which AMD has acknowledged, could cause issues in specific scenarios. The kernel patch in 6.18-rc4 now disables the use of RDSEED on affected Zen 5 CPUs that are running older microcode, preventing potential system instability. This is a vital software-level fix until all users receive the updated microcode from AMD.
Preparing for AMD Zen 6
Looking even further ahead, Linux 6.18-rc4 expands the kernel’s hardware support by adding more model IDs for AMD’s future Zen 6 processor family. While Zen 6 hardware is not yet available, adding these IDs so early in the development cycle ensures that Linux will be ready to support these next-generation CPUs from day one.
Power Management Performance Regression Fixed
Beyond the AMD-specific changes, 6.18-rc4 also addresses a performance regression reported by some users on Intel systems.
As reported by PHORONIX, a change in the cpuidle menu governor (which manages how a CPU core enters low-power states) introduced in kernel 6.17 caused an 11% throughput regression in certain workloads. This issue has now been identified and fixed. The patch, which is part of 6.18-rc4, adjusts the governor’s logic to prevent it from choosing overly latent idle states, restoring full performance for affected users.
What This Means for You
If you are a regular user on a stable distribution like Fedora 43 or Ubuntu 25.10, you don’t need to do anything. These changes are part of the development kernel and will be backported to stable kernels if necessary (like the Zen 5 fix) or will simply be part of the final Linux 6.18 release, which is expected to land in late November or early December 2025.
For enthusiasts and “bleeding-edge” users who are already testing release candidates, 6.18-rc4 is a recommended update, especially if you were affected by the power management regression or are testing new Zen 5 hardware.
It’s important to differentiate this development release from the stable updates. If you are not a tester, you should instead focus on the NEW STABLE KERNEL UPDATES (6.17.7, 6.12.57) THAT WERE ALSO RELEASED TODAY, which contain vital security and bug fixes for your current system.
Are you tracking the development of Linux 6.18? What features are you most excited about? Have you ever run a “Release Candidate” kernel on your system? Share your experiences in the comments section below!