Chapter 5. Important changes to external kernel parameters

This chapter provides system administrators with a summary of significant changes in the kernel distributed with Red Hat Enterprise Linux 9.8. These changes could include, for example, added or updated proc entries, sysctl, and sysfs default values, boot parameters, kernel configuration options, or any noticeable behavior changes.

New kernel parameters

Disable Memory Partitioning and Monitoring (MPAM) support on systems that support MPAM but do not enable it in firmware.

Show missing controllers in /proc/cgroups.

Format: { "true" | "false" }

By default, /proc/cgroups lists only cgroup v1 controllers. This compatibility option also lists v2 controllers (whose v1 code is not compiled) so that semi-legacy software can use this file to decide whether to use v2 controllers.

Specify mount options for the initramfs mount.

Extend the built-in NVMe quirk list.

Format: VendorID:ProductID:quirk_names[-VendorID:ProductID:quirk_names…​]

The IDs are 4-digit hexadecimal numbers. The quirk_names field is a comma-separated list of quirk names. Prefix a quirk name with ^ to disable the specified quirk.

For example:

nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi

Control waived items in Red Hat Enterprise Linux.

Some features or security mitigations can be waived and toggled on or off on demand. Waive these items only when necessary, because this can make the system insecure or out of support scope.

Format: <item-1>,<item-2>…​<item-n>

Use rh_waived to enable all waived features that Documentation/admin-guide/rh-waived-features.rst lists.

Control mitigation for VMscape attacks.

VMscape attacks can leak information from a user space hypervisor to a guest by using speculative side channels.

Possible values:

Changed kernel parameters

Control the behavior of the microcode loader.

You can specify the following options as a comma-separated list:

Control optional mitigations for CPU vulnerabilities.

This kernel parameter is a set of curated, architecture-independent options. Each option aggregates architecture-specific parameters.

Possible values:

On x86, after you specify one of the preceding options, you can also use attack-vector-based controls as described in Documentation/admin-guide/hw-vuln/attack_vector_controls.rst.