While there are ways to disable mitigation against many of the side-channel issues, this is not one of them. I believe this one is mitigated by the "sbb;and" sequence here:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...

There is no way to enable or disable this particular mitigation. That's probably because it's an extremely cheap mitigation.

Disclaimer: I work on Linux at Intel.