Re: Writable module parameters in KVM

[Paolo Bonzini]

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.

Paolo