rdos wrote:For one, it will break everything that runs today, perhaps excluded 64-bit EFI OSes that only use a single processor core.
That's fine, there's still plenty of time for current OSes to be updated.
rdos wrote:There is no logic in why CS, DS, ES and SS cannot handle segment loads (when FS and GS still must). This probably leads to more complexity not less.
CS, DS, ES, and SS are all implicitly used by various instruction addressing modes. All of that logic - which can't be entirely in microcode because it's so fundamental to x86 - can be simplified because the implicit segment no longer matters; only explicit FS and GS prefixes can impact the effective address.
rdos wrote:There is also no logic why protected mode (compability mode) cannot work in kernel space, and there is additionally no logic why only two rings would be supported. This doesn't lead to a less complex processor, rather to the contrary since these cases must be detected and caused to fault.
You're either underestimating the complexity of all those rarely-used modes or overestimating the complexity of faulting on attempts to switch to them.
rdos wrote:I cannot see this being implemented in a real CPU anytime soon.
It won't be. This kind of change takes a while to make it to hardware.
rdos wrote:First, all OSes that want to operate on it will need to handle how to start additional cores, and the new method described doesn't work on today's CPUs.
That's fine, ACPI provides a method that does work on today's CPUs. The only part that has to change is the switch between 4-level and 5-level paging.
rdos wrote:Forget about GRUB and legacy booting, which many modern BIOSes still support.
You know GRUB supports UEFI, right? And many modern PCs no longer include a CSM (or it doesn't work because some component doesn't have a legacy option ROM). Multiboot won't work, but Multiboot was never very good in the first place.
rdos wrote:Hopefully, AMD will not break protected mode like this, and then I can still run my OS on AMD.
AMD is definitely going to follow Intel's lead here.