Edd BarrettJan 20, 2023

Some quick notes from the paper "Performance implications of system management mode" by Delgado et al.

X86_46 system management mode (SMM) is invoked by a special (totally unmaskable) SMI interrupt.

When an SMI occurs, all cores are interrupted. One core executes a handler while the other cores wait.

It's used for stuff like power /heat management, hardware emulation and more recently security checkers.

Show threadEdd BarrettJan 20, 2023
SMI handlers can disrupt the OS' scheduler ticks, causing either delayed or (if the handler is long enough) missed ticks.
Show threadEdd Barrett
For a tickless kernel, SMM will wake up sleeping cores, often just so they can wait for the handler to finish.
Jan 20, 2023 at 10:33amWeb
Show threadEdd BarrettJan 20, 2023
The authors were able to make audio skip, graphics rendering degrade by injecting SMIs.
Show threadEdd BarrettJan 20, 2023
Intel suggests a maximum time budget for a SMI handler, but several security checkers are known to take much longer.