Well yes. That is why the "prefetch" is a problem. But the original question was asking why disabling data prefetching to a memory region didn't automatically

Well yes. That is why the "prefetch" is a problem. But the original question was asking why disabling data prefetching to a memory region didn't automatically disable instruction prefetching at the same time. And the answer is that speculative execution is a completely different mechanism that I'm not even sure can be disabled, at least not per memory region.