A solution seems to exist. This turns out to be a host IOMMU issue.
Notwithstanding that Intel VT-x and VT-d are enabled in the host firmware, kernel version 5.15.0-46-generic disables IOMMU by default. The kernel is configured with:
CONFIG_INTEL_IOMMU=y
# CONFIG_INTEL_IOMMU_DEFAULT_ON is not set
That is, intel_iommu is compiled into the kernel but not (or no longer is) enabled by default (note the octothorpe commenting out the second configuration option).
Adding the following to the kernel command line fixes the guest freezes and kcompactd0 no longer pins its CPU core at 100%, at least thus far:
intel_iommu=on
So, for GRUB, edit /etc/default/grub to add the above string to GRUB_CMDLINE_LINUX_DEFAULT, e.g.,
GRUB_CMDLINE_LINUX_DEFAULT="intel_iommu=on"
Save and close the file, then run:
# update-grub
Reboot to take effect.
For systemd-boot, either (a) add the above string to a separate line in /etc/kernel/cmdline or (b) add the following to your boot entry .conf file in /loader/entries:
options intel_iommu=on
Save and close the file, then reboot to take effect.
