With Unbreakable Enterprise Kernel Release 5 Update 4, Oracle continues to deliver kernel modifications to enable support for 64-bit Arm (aarch64) architecture. These changes are built and tested against existing Arm hardware and provide support for Oracle Linux for Arm. Features described in this document are available for Arm insofar as the hardware is capable of supporting the feature that is described. Limitations and items that are beyond the scope of current development work for Arm are described in more detail in Unusable or Unavailable Features for Arm.

UEK R5U4 provides equivalent core kernel functionality to UEK R5U3, making use of the same upstream mainline kernel release and upstream LTS bug fixes, with additional patches to enhance existing functionality and provide some minor bug fixes and security improvements. Key changes are specific to functionality that is required for Oracle Database and other Oracle software.

Kernel patching is applied to enable a feature that allows reservation of process virtual address ranges. This feature is specifically developed to improve Oracle Database stability when ASLR (Address Space Layout Randomization) is enabled. Kernel and user space interfaces are available to reserve memory ranges and allocate memory map from these ranges when a user space task requires. This feature is available for ELF64 binary objects only and its support and use case is currently limited to Oracle Database.

The following notable DTrace features and fixes are implemented in UEK R5U4:

• Fix for tail recursion in dtrace_dynvar()

  A fix was applied for an issue where lengthy tail recursion in dtrace_dynvar() could lead to an out-of-stack crash when the kernel stack is overrun with many recursion calls.

The following notable file system changes are implemented in UEK R5U4:

• Btrfs

  General upstream bug fixes are back-ported into this kernel update release.

• CIFS

  Upstream bug fixes are included, along with a fix to a specific bug that could prevent CIFS mounts when using Distributed File Systems (DFS).

• Ext4

  Multiple upstream bug fixes are back-ported into this kernel update release.

• NFS

  NFS is updated with several upstream fixes, along with improvements and optimizations for page cache and RPC call handling . Bug fixes that resolve a number of issues that could result in NFSv4 clients losing lease expiry state or obtaining incorrect lease expiry information were also back-ported from the upstream kernel.

• OCFS2

  Issues with the NFS kernel server when hosted on OCFS2 are resolved. In particular, patches are applied to prevent inode removal while nfsd is accessing the inode.

• XFS

  XFS is updated to include upstream patches, including security fixes and general bug fixes. Notably, a fix is applied for a file system freeze that could cause a system to hang. . Also, as part of this update, a bug was fixed to fix and improve ratelimiting code that could result in a race condition when inode flushing.

UEK R5U4 supports 1/10/25/50/100 Gb Ethernet ports. 200 Gb Ethernet ports are not enabled in UEK R5U4 as the changes required to support this affect the kernel ABI. Oracle maintains kernel ABI compatibility through the duration of the UEK R5 lifecycle. If you require the use of 200 Gb Ethernet ports use UEK R6.

The following additional enhancements and feature changes are in place for networking functionality in this update release:

• Enhanced TCP Stack for diagnostics

  Enhancements are added to the TCP stack to facilitate better diagnostics through extended Berkeley Packet Filter (eBPF) tracepoints along with several optimizations that allow more rapid diagnostics and testing, but also to reduce performance overhead related to tracing.

The following notable security features are implemented in Unbreakable Enterprise Kernel Release 5 Update 4:

• Spectre-v1 mitigation extensions

  Patches available in the upstream Linux 5.6 kernel are included to extend Spectre-v1 mitigation by preventing index computations from causing speculative loads into the L1 cache.