> The AMD microarchitecture does not allow memory references, including speculative references, that access higher privileged data when running in a lesser privileged mode when that access would result in a page fault.
Out-of-order processors generally trigger exceptions when instructions are retired. Because instructions are retired in-order, that allows exceptions and interrupts to be reported in program order, which is what the programmer expects to happen. Furthermore, because memory access is a critical path, the TLB/privilege check is generally started in parallel with the cache/memory access. In such an architecture, it seems like the straightforward thing to do is to let the improper access to kernel memory execute, and then raise the page fault only when the instruction retires.
