The update of the TIF_SSBD flag and the conditional speculation control MSR
update is done in the ssb_prctl_set() function directly. The upcoming prctl
support for controlling indirect branch speculation via STIBP needs the
same mechanism.

Split the code out and make it reusable.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/cpu/bugs.c |   31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -703,10 +703,25 @@ static void ssb_select_mitigation(void)
 #undef pr_fmt
 #define pr_fmt(fmt)     "Speculation prctl: " fmt
 
-static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
+static void task_update_spec_tif(struct task_struct *tsk, int tifbit, bool on)
 {
 	bool update;
 
+	if (on)
+		update = !test_and_set_tsk_thread_flag(tsk, tifbit);
+	else
+		update = test_and_clear_tsk_thread_flag(tsk, tifbit);
+
+	/*
+	 * If being set on non-current task, delay setting the CPU
+	 * mitigation until it is scheduled next.
+	 */
+	if (tsk == current && update)
+		speculation_ctrl_update_current();
+}
+
+static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
+{
 	if (ssb_mode != SPEC_STORE_BYPASS_PRCTL &&
 	    ssb_mode != SPEC_STORE_BYPASS_SECCOMP)
 		return -ENXIO;
@@ -717,28 +732,20 @@ static int ssb_prctl_set(struct task_str
 		if (task_spec_ssb_force_disable(task))
 			return -EPERM;
 		task_clear_spec_ssb_disable(task);
-		update = test_and_clear_tsk_thread_flag(task, TIF_SSBD);
+		task_update_spec_tif(task, TIF_SSBD, false);
 		break;
 	case PR_SPEC_DISABLE:
 		task_set_spec_ssb_disable(task);
-		update = !test_and_set_tsk_thread_flag(task, TIF_SSBD);
+		task_update_spec_tif(task, TIF_SSBD, true);
 		break;
 	case PR_SPEC_FORCE_DISABLE:
 		task_set_spec_ssb_disable(task);
 		task_set_spec_ssb_force_disable(task);
-		update = !test_and_set_tsk_thread_flag(task, TIF_SSBD);
+		task_update_spec_tif(task, TIF_SSBD, true);
 		break;
 	default:
 		return -ERANGE;
 	}
-
-	/*
-	 * If being set on non-current task, delay setting the CPU
-	 * mitigation until it is next scheduled.
-	 */
-	if (task == current && update)
-		speculation_ctrl_update_current();
-
 	return 0;
 }