[caf]

The MELTDOWN one is the easy one (as is evident by the fact that this is the one that only seems to affect Intel CPUs).

When a load is found to be illegal, an exception flag is set so that if the instruction is retired (ie. the speculated execution is found to be the actual path taken), a page fault exception can be raised. To prevent MELTDOWN, at the same time that the flag is raised you can set the result of the load to zero.

SPECTRE is the really hard one to deal with. Part of the solution might be providing a way for software to flush the branch predictor state.

[ant6n]

Maybe separate BTBs. Or maybe disable branch target prediction when in kernel mode (but then some VM process may still observe some other process running inside a different VM via a side channel).