As a late change that was merged yesterday for the Linux 5.4 kernel that will be released in the next few weeks, Xen 32-bit PV guest support has been deprecated.

SUSE's Juergen Gross deprecation notice was accepted on Friday by Linus Torvalds for Linux 5.4. When configuring the kernel build with Xen para-virtualized support for x86 32-bit, the following warning will now be produced:

WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING!
Support for running as 32-bit PV-guest under Xen will soon be removed
from the Linux kernel!
Please use either a 64-bit kernel or switch to HVM or PVH mode
WARNING! WARNING! WARNING! WARNING! WARNING! WARNING! WARNING!

The old days of 32-bit x86 servers...

Xeon LV days...

This deprecation possibility has been talked about for months, so it shouldn't exactly come as a surprise. If still running 32-bit, the HVM/PVH modes will continue to be supported for the foreseeable future. If still running x86_32 as the host system as opposed to just 32-bit VMs, especially with the likes of x86 32-bit not being fully mitigated for the speculative execution vulnerabilities (e.g. Meltdown) and the power inefficiencies and overall sluggishness of older 32-bit x86 processors, if still running them it may be time to consider upgrading especially for virtualization use.