Function with_flush 

unsafe fn with_flush<T>(flush: u32, work: impl FnOnce() -> T) -> T

Run work with the flushing bits flush & FLUSH on the current thread, then restore the caller’s flushing bits, also while unwinding a panic.

The writes take pointers to work and to its result, which keeps the work between them (see the module’s soundness section).

Safety

The processor implements every bit of flush & FLUSH.