message: Set CR3 in entry.asm also when booting the Application Processor.
  This finally fixes booting an Application Processor in HermitCore-rs running on uhyve.
diff: @@ -137,20 +137,27 @@ start64:
  add rsp, (KERNEL_STACK_SIZE - 0x10)
  mov rbp, rsp
  - ; Is this an Application Processor?
  - xor rax, rax
  + ; Assume and then check whether this is an Application Processor.
  + ; Skip boot processor initialization steps in this case.
  + mov r8, application_processor_main
  mov eax, DWORD [cpu_online]
  cmp eax, 0
  - je boot_processor_init
  -
  - ; Then we're done and just call into the Application Processor Rust entry point.
  - call application_processor_main
  - jmp $
  + jne boot_processor_init_done
  boot_processor_init:
  + ; Overwrite the entry point to call.
  + mov r8, boot_processor_main
  +
  ; store pointer to the multiboot information
  mov [mb_info], QWORD rdx
  + ; Set EFER.NXE to enable early access to EXECUTE_DISABLE-protected memory.
  + ; For the Application Processor, this has already been done in boot.asm or by uhyve.
  + mov ecx, MSR_EFER
  + rdmsr
  + or eax, EFER_NXE
  + wrmsr
  +
  ; relocate page tables
  mov rdi, boot_pml4
  mov rax, QWORD [rdi]
  @@ -202,25 +209,21 @@ Lremap:
  add rdi, 8
  ; note: the whole code segement has to fit in the first pgd
  cmp rcx, rsi
  - jnl Lremap_done
  + jnl boot_processor_init_done
  cmp rcx, r11
  jl Lremap
  -Lremap_done:
  +boot_processor_init_done:
  ; Set CR3
  + ; If this is an Application Processor and we're running bare-metal/QEMU, this has already been done in boot.asm.
  + ; However, this step is required when running on uhyve.
  mov rax, boot_pml4
  sub rax, kernel_start
  add rax, [base]
  mov cr3, rax
  - ; Set EFER.NXE to enable early access to EXECUTE_DISABLE-protected memory.
  - mov ecx, MSR_EFER
  - rdmsr
  - or eax, EFER_NXE
  - wrmsr
  -
  - ; Call into the Boot Processor Rust entry point.
  - call boot_processor_main
  + ; Call into the desired Rust entry point.
  + call r8
  jmp $
  ; NASM macro for asynchronous interrupts (no exceptions)
  