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Chapter 4. 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 7.9. These changes include added or updated proc entries, sysctl, and sysfs default values, boot parameters, kernel configuration options, or any noticeable behavior changes.

4.1. New kernel parameters

bert_disable [ACPI]

This parameter disables Boot Error Record Table (BERT) on defective BIOSes.

BERT is one of four ACPI Platform Error Interface tables and is used for obtaining hardware error logs that occurred in the previous boot and firmware did not notify the kernel about the error at runtime, for example through a non-maskable interrupt (NMI) or a machine-check exception (MCE).

bert_enable [ACPI]
RHEL7 only. This parameter enables Boot Error Record Table (BERT). The default state is disabled.
page_owner = [KNL]

Storage of the information about who allocated each page is disabled in default. This parameter enables to store such information by using the following option:

  • on - enable the feature
srbds = [X86,INTEL]

This parameter controls the Special Register Buffer Data Sampling (SRBDS) mitigation.

Certain CPUs are vulnerable to MDS-like (Microarchitectural Data Sampling) exploits which can leak bits from the random number generator.

By default, this issue is mitigated by microcode. However, the microcode fix can cause the RDRAND (read random) and RDSEED instructions to become much slower. Among other effects, this will result in reduced throughput from the /dev/urandom file.

The microcode mitigation can be disabled with the following option:

  • off - Disable mitigation and remove performance impact to RDRAND and RDSEED.

4.2. New /proc/sys/kernel/ parameters

hyperv_record_panic_msg

This parameter controls whether the panic kernel (kmsg) data is reported to Hyper-V or not.

The values are:

  • 0 - Do not report the panic kmsg data.
  • 1 - Report the panic kmsg data. This is the default behavior.