One more thing, I think this is all related to this message when booting the Debian PREEMPT_RT kernel: [ 0.556708] efi: EFI_MEMMAP is not enabled. When compiling the EFI options into kernel (Y) instead of a module (M) the message disappears but the problem remains. Switching between the signed and unsigned preempt_rt kernel packages have no effect. Sorry for the noise. Alec
