I have a couple question about Meltdown and the Intel chips. My understanding is that a key part of this is that upon speculative execution the page table permi

I have a couple question about Meltdown and the Intel chips. My understanding is that a key part of this is that upon speculative execution the page table permission checks only happen when the "transient"instruction is retired. Was this simply a performance engineering trade off made by Intel? Would checking the PTE permissions on speculative execution result in giving up any performance gained by the speculative execution?