I enjoyed reading this a lot. I wonder why the developers decided to allow reading kernel-memory in the first place. When a scalar processor reads kernel memory, it crashes. When a speculative processor reads kernel memory, it relies on the assumption that the read is never committed to prevent leakage. It takes no expert to realise this is a potentially dangerous decision (and, as becomes clear now, is only valid in the absence of a cache).
To me it would make a lot more sense to use a special value to indicate the read did not succeed and propagate this value until it is time to crash. I guess this introduces some overhead (e.g. reserve a special value); but are there any other drawbacks?