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

*** 21,31 ****
  /*
   * Copyright (c) 2012 Gary Mills
   *
   * Copyright (c) 1993, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright (c) 2011 by Delphix. All rights reserved.
!  * Copyright 2016 Joyent, Inc.
   */
  /*
   * Copyright (c) 2010, Intel Corporation.
   * All rights reserved.
   */
--- 21,31 ----
  /*
   * Copyright (c) 2012 Gary Mills
   *
   * Copyright (c) 1993, 2010, Oracle and/or its affiliates. All rights reserved.
   * Copyright (c) 2011 by Delphix. All rights reserved.
!  * Copyright 2018 Joyent, Inc.
   */
  /*
   * Copyright (c) 2010, Intel Corporation.
   * All rights reserved.
   */
*** 146,156 ****
--- 146,177 ----
          if (bootprop_getval("cpuid_feature_edx_exclude", &prop_value) != 0)
                  cpuid_feature_edx_exclude = 0;
          else
                  cpuid_feature_edx_exclude = (uint32_t)prop_value;
  
+ #if !defined(__xpv)
          /*
+          * Check to see if KPTI has been explicitly enabled or disabled.
+          * We have to check this before init_desctbls().
+          */
+         if (bootprop_getval("kpti", &prop_value) == 0) {
+                 kpti_enable = (uint64_t)(prop_value == 1);
+                 prom_printf("unix: forcing kpti to %s due to boot argument\n",
+                     (kpti_enable == 1) ? "ON" : "OFF");
+         } else {
+                 kpti_enable = 1;
+         }
+ 
+         if (bootprop_getval("pcid", &prop_value) == 0 && prop_value == 0) {
+                 prom_printf("unix: forcing pcid to OFF due to boot argument\n");
+                 x86_use_pcid = 0;
+         } else if (kpti_enable != 1) {
+                 x86_use_pcid = 0;
+         }
+ #endif
+ 
+         /*
           * Initialize idt0, gdt0, ldt0_default, ktss0 and dftss.
           */
          init_desctbls();
  
          /*