The good news: There's a new MSR which lets you do this:

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

The less good news: as far as I can tell, Intel did not commit to how architectural this will be going forward. Considering the role TSX has played in speculation-based attacks, it appears to me to be a generic mitigation that would be great to accompany TSX wherever it is available in the future. Now that MSR_IA32_TSX_CTRL is defined, it should be easier to implement going forward.

Disclaimer: I work on Linux at Intel.