[PATCH] x86/bugs: Fix handling when srso mitigation is disabled

[David Kaplan]

When the srso mitigation is disabled, either via mitigations=off or
spec_rstack_overflow=off, SBPB should be used instead of IBPB if
possible.  Additionally, move the check earlier in the function so no
warning is printed about the lack of IBPB-enhancing microcode since the
user has turned off the mitigation.

Signed-off-by: David Kaplan <david.kaplan@xxxxxxx>
---
 arch/x86/kernel/cpu/bugs.c | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 189840db2f8d..10d0775e7aa5 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2557,10 +2557,9 @@ static void __init srso_select_mitigation(void)
 {
 	bool has_microcode = boot_cpu_has(X86_FEATURE_IBPB_BRTYPE);
 
-	if (cpu_mitigations_off())
-		return;
-
-	if (!boot_cpu_has_bug(X86_BUG_SRSO)) {
+	if (!boot_cpu_has_bug(X86_BUG_SRSO) ||
+	     cpu_mitigations_off() ||
+	     srso_cmd == SRSO_CMD_OFF) {
 		if (boot_cpu_has(X86_FEATURE_SBPB))
 			x86_pred_cmd = PRED_CMD_SBPB;
 		return;
@@ -2591,11 +2590,6 @@ static void __init srso_select_mitigation(void)
 	}
 
 	switch (srso_cmd) {
-	case SRSO_CMD_OFF:
-		if (boot_cpu_has(X86_FEATURE_SBPB))
-			x86_pred_cmd = PRED_CMD_SBPB;
-		return;
-
 	case SRSO_CMD_MICROCODE:
 		if (has_microcode) {
 			srso_mitigation = SRSO_MITIGATION_MICROCODE;
@@ -2649,6 +2643,8 @@ static void __init srso_select_mitigation(void)
 			pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
                 }
 		break;
+	default:
+		break;
 	}
 
 out:
-- 
2.34.1