[MelioRatio]

You can actually do that fairly easily, just add the parameters linked to a second boot entry in GRUB.

However, I would very much not advise doing so, as I still am unaware of any task that can both, be done without the need for a network connection, while also being significantly slowed down by the mitigations, after recent improvements to the kernel and software. Basically, the potential benefit is very low in a lot of tasks, whilst requiring additional security measures (ideally fully air-gapped) and that you reboot the system every time you'd do such a task.

Also note that, in theory, just being temporarily offline may not shield from being exploited fully.

[bryanbuckley]

As an example (the only case that I've identified personally), if your curious, I have a (windows; Intel q6600) box that I use for gaming occasionally. Single player game I like, Total War: Shogun 2, runs at about 55 fps (benchmark) pre-Meltdown/Spectre/etc. Now it gets ~22 fps. I can use https://www.grc.com/inspectre.htm to toggle some mitigations to get it playable again.