I very much don't understand why Intel didn't disable AVX-512 on the P cores, unless and until the OS writes to a new MSR that means "I understand that the P cores can do AVX-512, while the E cores cannot", and then enable AVX-512 on the P cores.
Old OS versions continue to work fine, and newer OS versions can opt into the new world and benefit.
Old OS versions continue to work fine, and newer OS versions can opt into the new world and benefit.