Re: Writable module parameters in KVM

From: Paolo Bonzini
Date: Wed May 26 2021 - 06:49:23 EST

On 26/05/21 01:45, Ben Gardon wrote:

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.

Sure, making them writable is okay. Most KVM parameters are read-only because it's much simpler (the usecase for introducing them was simply "test what would happen on old processors"). What are these features that you'd like to control?

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?

They probably should, yes.