At Google we have an informal practice of adding sysctls to control some KVM features. Usually these just act as simple "chicken bits" which allow us to turn off a feature without having to stall a kernel rollout if some feature causes problems. (Sysctls were used for reasons specific to Google infrastructure, not because they're necessarily better.)
We'd like to get rid of this divergence with upstream by converting the sysctls to writable module parameters, but I'm not sure what the general guidance is on writable module parameters. Looking through KVM, it seems like we have several writable parameters, but they're mostly read-only.
I also don't see central documentation of the module parameters. They're mentioned in the documentation for other features, but don't have their own section / file. Should they?