On Tue, Feb 28 2023 at 21:57, David Woodhouse wrote: > On Tue, 2023-02-28 at 22:01 +0100, Thomas Gleixner wrote: > Empirically, yours doesn't boot and Brian's does. Correct. It was just my sleep deprived brain which got lost in assembly and #ifdef maze. On UP per_cpu variables just become regular variables and gdt_page(%rdx) with %rdx = 0 will just resolve that address. Sorry for the noise. Thanks, tglx