[patch 21/24] x86/speculation: Prepare arch_smt_update() for PRCTL mode

[Thomas Gleixner]

The upcoming fine grained per task STIBP control needs to be updated on CPU
hotplug as well.

Split out the code which controls the strict mode so the prctl control code
can be added later.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/bugs.c |   46 ++++++++++++++++++++++++---------------------
 1 file changed, 25 insertions(+), 21 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -531,40 +531,44 @@ static void __init spectre_v2_select_mit
 	arch_smt_update();
 }
 
-static bool stibp_needed(void)
+static void update_stibp_msr(void *info)
 {
-	/* Enhanced IBRS makes using STIBP unnecessary. */
-	if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
-		return false;
-
-	/* Check for strict app2app mitigation mode */
-	return spectre_v2_app2app == SPECTRE_V2_APP2APP_STRICT;
+	wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
 }
 
-static void update_stibp_msr(void *info)
+/* Update x86_spec_ctrl_base in case SMT state changed. */
+static void update_stibp_strict(void)
 {
-	wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+	u64 mask = x86_spec_ctrl_base & ~SPEC_CTRL_STIBP;
+
+	if (sched_smt_active())
+		mask |= SPEC_CTRL_STIBP;
+
+	if (mask == x86_spec_ctrl_base)
+		return;
+
+	pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n",
+		mask & SPEC_CTRL_STIBP ? "Enabling" : "Disabling");
+	x86_spec_ctrl_base = mask;
+	on_each_cpu(update_stibp_msr, NULL, 1);
 }
 
 void arch_smt_update(void)
 {
-	u64 mask;
-
-	if (!stibp_needed())
+	/* Enhanced IBRS makes using STIBP unnecessary. No update required. */
+	if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
 		return;
 
 	mutex_lock(&spec_ctrl_mutex);
 
-	mask = x86_spec_ctrl_base & ~SPEC_CTRL_STIBP;
-	if (sched_smt_active())
-		mask |= SPEC_CTRL_STIBP;
-
-	if (mask != x86_spec_ctrl_base) {
-		pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n",
-			mask & SPEC_CTRL_STIBP ? "Enabling" : "Disabling");
-		x86_spec_ctrl_base = mask;
-		on_each_cpu(update_stibp_msr, NULL, 1);
+	switch (spectre_v2_app2app) {
+	case SPECTRE_V2_APP2APP_NONE:
+		break;
+	case SPECTRE_V2_APP2APP_STRICT:
+		update_stibp_strict();
+		break;
 	}
+
 	mutex_unlock(&spec_ctrl_mutex);
 }