As someone who has written a jit compiler, I am puzzled by the claim that jitting requires write/execute permissions. When I have written a jit, I loaded some memory with read/write permissions using mmap. Once I filled in the generated code, I mprotected the region to read/execute before executing.

The drawback to this approach is there can be some bloat because you can only mprotect at page granulariy so a jitted function that only takes say 10 bytes to represent would take up a full page in memory, but this is extreme and in practice, the overhead is unlikely to be worth worrying about.