Version
Seen on systemd 219-67 but still exist in master

Used distribution
Centos

Expected behaviour you didn't see
Running /usr/bin/udevadm trigger --type=devices --action=add pollutes the kernel logs.
On a Dual AMD-7702, this commands prints 256 times "kvm: disabled by bios"
An "add" event to /sys/devices/system/cpu/cpu/uevent will print this message.
As my system has CPU 256 threads, this prints 256 times that line in the logs.
That clearly pollutes the logs.

Unexpected behaviour you saw
I would expect /usr/bin/udevadm trigger to only perform the "add" on a single cpu thread, not on all of them.

Steps to reproduce the problem
Run "/usr/bin/udevadm trigger --type=devices --action=add" on a system where the virtualization extensions are off, you'll get one line per cpu thread existing on the system.