9723 provide support for VMM's GDT handling
Reviewed by: Robert Mustacchi <rm@joyent.com>
Reviewed by: Patrick Mooney <patrick.mooney@joyent.com>

*** 1288,1298 ****
--- 1288,1320 ----
          kpti_safe_cr3 = (uint64_t)getcr3();
  }
  
  #endif  /* __xpv */
  
+ #ifndef __xpv
  /*
+  * As per Intel Vol 3 27.5.2, the GDTR limit is reset to 64Kb on a VM exit, so
+  * we have to manually fix it up ourselves.
+  *
+  * The caller may still need to make sure that it can't go off-CPU with the
+  * incorrect limit, before calling this (such as disabling pre-emption).
+  */
+ void
+ reset_gdtr_limit(void)
+ {
+         ulong_t flags = intr_clear();
+         desctbr_t gdtr;
+ 
+         rd_gdtr(&gdtr);
+         gdtr.dtr_limit = (sizeof (user_desc_t) * NGDT) - 1;
+         wr_gdtr(&gdtr);
+ 
+         intr_restore(flags);
+ }
+ #endif /* __xpv */
+ 
+ /*
   * In the early kernel, we need to set up a simple GDT to run on.
   *
   * XXPV Can dboot use this too?  See dboot_gdt.s
   */
  void