Kernel Issues

The following are known kernel issues that have been encountered in this release of Oracle Linux 8.

KVM guests boot with "amd64_edac_mod: Unknown symbol" errors on AMD 64-Bit platforms

The following errors might be displayed repeatedly when KVM guests are booting on 64-bit AMD hosts:

[   12.474069] amd64_edac_mod: Unknown symbol amd_register_ecc_decoder (err [ 120)
[   12.474083] amd64_edac_mod: Unknown symbol amd_report_gart_errors (err 0)
[   12.852250] amd64_edac_mod: Unknown symbol amd_unregister_ecc_decoder (err 0)
[   12.852297] amd64_edac_mod: Unknown symbol amd_register_ecc_decoder (err 0)
.
.
.

These errors occur because the module code for the kernel erroneously returns -EEXIST for modules that failed to load and are in the process of being removed from the module list. The amd64_edac_mod module will not be loaded in a VM. These errors can be ignored, as they do not impact functionality in any way.

This issue occurs on Oracle Linux 8 hosts that are running RHCK only and is not encountered on UEK R6 hosts.

(Bug ID 29853602)

Output of modinfo command doesn't show retpoline support

A bug in the Oracle Linux 8 code causes Retropline support to not be displayed in the output of the modinfo -F retpoline command, even though the CONFIG_RETPOLINE flag is set to Y, for example:

sudo modinfo -F retpoline
/usr/lib/modules/4.18.0-80.el8.x86_64/kernel/sound/usb/usx2y/snd-usb-us122l.ko
.xz

The CONFIG_RETPOLINE=Y flag is still required to add and display Retpoline support. If the parameter is enabled, the kernel builds with a retpoline capable compiler.

To confirm that the CONFIG_RETPOLINE flag is enabled, search for the parameter in the kernel's config-kernel configuration file, for example:

cat /boot/config-5.4.17-2011.7.4.el8uek.x86_64 | grep RETPOLINE.

CONFIG_RETPOLINE=y

(Bug ID 29894295)

Kdump Might Fail on Some AMD Hardware

Kdump might fail on some AMD hardware that is running the current Oracle Linux release. Impacted hardware includes the AMD EPYC CPU servers.

To work around this issue, modify the /etc/sysconfig/kdump configuration file and remove the iommu=off command-line option from the KDUMP_COMMANDLINE_APPEND variable. Restart the kdump service for the changes to take effect.

(Bug ID 31274238, 34312626)

Limitations of the LVM dm-writecache Caching Method

The new LVM dm-writecache caching method has certain limitations that don't exist with the dm-cache method, including the following:

• Can't attach or detach dm-writecache when a logical volume is active.

• Can't take a snapshot of a logical volume when the logical volume is using dm-writecache.

• Must use a dm-writecache block size that matches the existing file system block size when attaching dm-writecache to an inactive logical volume.

• Can't resize a logical volume when dm-writecache is attached to the volume.

• Can't use pvmove commands on devices that are used with dm-writecache.

• Can't use logical volumes with dm-writecache when using thin pools or the virtual data optimizer (VDO).

For more information about the dm-writecache caching method, see the File Systems and Storage features section of Oracle Linux 8: Release Notes for Oracle Linux 8.2. See also the lvmcache(7) manual page.