9685 KPTI %cr3 handling needs fixes

@@ -364,18 +364,20 @@
         xc_call(0, 0, 0, CPUSET2BV(cpuset), (xc_func_t)kdi_cpu_deactivate);
         kdi_nmemranges = 0;
 }
 
 /*
- * We receive all breakpoints and single step traps.  Some of them,
- * including those from userland and those induced by DTrace providers,
- * are intended for the kernel, and must be processed there.  We adopt
- * this ours-until-proven-otherwise position due to the painful
- * consequences of sending the kernel an unexpected breakpoint or
- * single step.  Unless someone can prove to us that the kernel is
- * prepared to handle the trap, we'll assume there's a problem and will
- * give the user a chance to debug it.
+ * We receive all breakpoints and single step traps.  Some of them, including
+ * those from userland and those induced by DTrace providers, are intended for
+ * the kernel, and must be processed there.  We adopt this
+ * ours-until-proven-otherwise position due to the painful consequences of
+ * sending the kernel an unexpected breakpoint or single step.  Unless someone
+ * can prove to us that the kernel is prepared to handle the trap, we'll assume
+ * there's a problem and will give the user a chance to debug it.
+ *
+ * If we return 2, then the calling code should restore the trap-time %cr3: that
+ * is, it really is a kernel-originated trap.
  */
 int
 kdi_trap_pass(kdi_cpusave_t *cpusave)
 {
         greg_t tt = cpusave->krs_gregs[KDIREG_TRAPNO];

@@ -388,11 +390,11 @@
         if (tt != T_BPTFLT && tt != T_SGLSTP)
                 return (0);
 
         if (tt == T_BPTFLT && kdi_dtrace_get_state() ==
             KDI_DTSTATE_DTRACE_ACTIVE)
-                return (1);
+                return (2);
 
         /*
          * See the comments in the kernel's T_SGLSTP handler for why we need to
          * do this.
          */