diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
index 997d01944f91d5c84e4778c59b1ac429c814b4bb..b4b36e0f2e8960d3d195d9617576fe02a8d86f08 100644
--- a/arch/um/os-Linux/start_up.c
+++ b/arch/um/os-Linux/start_up.c
@@ -23,6 +23,7 @@
 #include "mem_user.h"
 #include "ptrace_user.h"
 #include "registers.h"
+#include "skas.h"
 #include "skas_ptrace.h"
 
 static void ptrace_child(void)
@@ -140,14 +141,27 @@ static int stop_ptraced_child(int pid, int exitcode, int mustexit)
 }
 
 /* Changed only during early boot */
-int ptrace_faultinfo = 1;
-int ptrace_ldt = 1;
-int proc_mm = 1;
-int skas_needs_stub = 0;
+int ptrace_faultinfo;
+static int disable_ptrace_faultinfo;
+
+int ptrace_ldt;
+static int disable_ptrace_ldt;
+
+int proc_mm;
+static int disable_proc_mm;
+
+int have_switch_mm;
+static int disable_switch_mm;
+
+int skas_needs_stub;
 
 static int __init skas0_cmd_param(char *str, int* add)
 {
-	ptrace_faultinfo = proc_mm = 0;
+	disable_ptrace_faultinfo = 1;
+	disable_ptrace_ldt = 1;
+	disable_proc_mm = 1;
+	disable_switch_mm = 1;
+
 	return 0;
 }
 
@@ -157,15 +171,12 @@ static int __init mode_skas0_cmd_param(char *str, int* add)
 	__attribute__((alias("skas0_cmd_param")));
 
 __uml_setup("skas0", skas0_cmd_param,
-		"skas0\n"
-		"    Disables SKAS3 usage, so that SKAS0 is used, unless \n"
-	        "    you specify mode=tt.\n\n");
+"skas0\n"
+"    Disables SKAS3 and SKAS4 usage, so that SKAS0 is used\n\n");
 
 __uml_setup("mode=skas0", mode_skas0_cmd_param,
-		"mode=skas0\n"
-		"    Disables SKAS3 usage, so that SKAS0 is used, unless you \n"
-		"    specify mode=tt. Note that this was recently added - on \n"
-		"    older kernels you must use simply \"skas0\".\n\n");
+"mode=skas0\n"
+"    Disables SKAS3 and SKAS4 usage, so that SKAS0 is used.\n\n");
 
 /* Changed only during early boot */
 static int force_sysemu_disabled = 0;
@@ -360,7 +371,7 @@ void __init os_early_checks(void)
 
 static int __init noprocmm_cmd_param(char *str, int* add)
 {
-	proc_mm = 0;
+	disable_proc_mm = 1;
 	return 0;
 }
 
@@ -372,7 +383,7 @@ __uml_setup("noprocmm", noprocmm_cmd_param,
 
 static int __init noptracefaultinfo_cmd_param(char *str, int* add)
 {
-	ptrace_faultinfo = 0;
+	disable_ptrace_faultinfo = 1;
 	return 0;
 }
 
@@ -384,7 +395,7 @@ __uml_setup("noptracefaultinfo", noptracefaultinfo_cmd_param,
 
 static int __init noptraceldt_cmd_param(char *str, int* add)
 {
-	ptrace_ldt = 0;
+	disable_ptrace_ldt = 1;
 	return 0;
 }
 
@@ -404,17 +415,15 @@ static inline void check_skas3_ptrace_faultinfo(void)
 
 	n = ptrace(PTRACE_FAULTINFO, pid, 0, &fi);
 	if (n < 0) {
-		ptrace_faultinfo = 0;
 		if (errno == EIO)
 			non_fatal("not found\n");
 		else
 			perror("not found");
-	}
+	} else if (disable_ptrace_faultinfo)
+		non_fatal("found but disabled on command line\n");
 	else {
-		if (!ptrace_faultinfo)
-			non_fatal("found but disabled on command line\n");
-		else
-			non_fatal("found\n");
+		ptrace_faultinfo = 1;
+		non_fatal("found\n");
 	}
 
 	stop_ptraced_child(pid, 1, 1);
@@ -437,38 +446,30 @@ static inline void check_skas3_ptrace_ldt(void)
 	if (n < 0) {
 		if (errno == EIO)
 			non_fatal("not found\n");
-		else {
+		else
 			perror("not found");
-		}
-		ptrace_ldt = 0;
-	}
+	} else if (disable_ptrace_ldt)
+		non_fatal("found, but use is disabled\n");
 	else {
-		if (ptrace_ldt)
-			non_fatal("found\n");
-		else
-			non_fatal("found, but use is disabled\n");
+		ptrace_ldt = 1;
+		non_fatal("found\n");
 	}
 
 	stop_ptraced_child(pid, 1, 1);
-#else
-	/* PTRACE_LDT might be disabled via cmdline option.
-	 * We want to override this, else we might use the stub
-	 * without real need
-	 */
-	ptrace_ldt = 1;
 #endif
 }
 
 static inline void check_skas3_proc_mm(void)
 {
 	non_fatal("  - /proc/mm...");
-	if (access("/proc/mm", W_OK) < 0) {
-		proc_mm = 0;
+	if (access("/proc/mm", W_OK) < 0)
 		perror("not found");
-	}
-	else if (!proc_mm)
+	else if (disable_proc_mm)
 		non_fatal("found but disabled on command line\n");
-	else non_fatal("found\n");
+	else {
+		proc_mm = 1;
+		non_fatal("found\n");
+	}
 }
 
 void can_do_skas(void)