Index: sys/x86/x86/mp_x86.c
===================================================================
--- sys/x86/x86/mp_x86.c
+++ sys/x86/x86/mp_x86.c
@@ -45,6 +45,7 @@
 #ifdef GPROF 
 #include <sys/gmon.h>
 #endif
+#include <sys/kdb.h>
 #include <sys/kernel.h>
 #include <sys/ktr.h>
 #include <sys/lock.h>
@@ -1269,6 +1270,12 @@
 	CPU_CLR_ATOMIC(cpu, &started_cpus);
 	CPU_CLR_ATOMIC(cpu, &stopped_cpus);
 
+	/*
+	 * We don't broadcast TLB invalidations to other CPUs when they are
+	 * stopped. Hence, we clear the TLB before resuming.
+	 */
+	invltlb_glob();
+
 #if defined(__amd64__) && defined(DDB)
 	amd64_db_resume_dbreg();
 #endif
@@ -1427,6 +1434,10 @@
 	uint32_t generation;
 	int cpu;
 
+	/* It is not necessary to signal other CPUs while in the debugger. */
+	if (kdb_active || panicstr != NULL)
+		return;
+
 	/*
 	 * Check for other cpus.  Return if none.
 	 */