8956 Implement KPTI
Reviewed by: Jerry Jelinek <jerry.jelinek@joyent.com>
Reviewed by: Robert Mustacchi <rm@joyent.com>

*** 24,34 ****
   * Use is subject to license terms.
   *
   * Copyright (c) 2010, Intel Corporation.
   * All rights reserved.
   *
!  * Copyright 2013 Joyent, Inc.  All rights reserved.
   */
  
  /*
   * This file contains the functionality that mimics the boot operations
   * on SPARC systems or the old boot.bin/multiboot programs on x86 systems.
--- 24,34 ----
   * Use is subject to license terms.
   *
   * Copyright (c) 2010, Intel Corporation.
   * All rights reserved.
   *
!  * Copyright 2018 Joyent, Inc.  All rights reserved.
   */
  
  /*
   * This file contains the functionality that mimics the boot operations
   * on SPARC systems or the old boot.bin/multiboot programs on x86 systems.
*** 845,854 ****
--- 845,860 ----
          static int firsttime = 1;
          bios_func_t bios_func = (bios_func_t)(void *)(uintptr_t)0x5000;
          bios_regs_t br;
  
          /*
+          * We're about to disable paging; we shouldn't be PCID enabled.
+          */
+         if (getcr4() & CR4_PCIDE)
+                 prom_panic("do_bsys_doint() with PCID enabled\n");
+ 
+         /*
           * The first time we do this, we have to copy the pre-packaged
           * low memory bios call code image into place.
           */
          if (firsttime) {
                  extern char bios_image[];