Update: Root cause found — HPET clocksource, not kernel 7.0
After further investigation, the high CPU usage was not caused by kernel 7.0 itself, but by the HPET (High Precision Event Timer) being used as the system clocksource.
Using perf top...
Kernel 7.0.0-2-pve will freeze the host if total free RAM becomes low (< 5 to 10% free). Any one seeing this issue? I just have to back off the RAM requirements for my VMs a little (now around 87% usage) and everything works again.
Host do not...