linux-kernel - [tip: x86/bugs] x86/bugs: Fix handling when SRSO mitigation is disabled

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Message-ID: <172552965872.2215.17085347492363546574.tip-bot2@tip-bot2>
Date: Thu, 05 Sep 2024 09:47:38 -0000
From: "tip-bot2 for David Kaplan" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: David Kaplan <david.kaplan@....com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, Josh Poimboeuf <jpoimboe@...nel.org>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject:
 [tip: x86/bugs] x86/bugs: Fix handling when SRSO mitigation is disabled

The following commit has been merged into the x86/bugs branch of tip:

Commit-ID:     1dbb6b1495d472806fef1f4c94f5b3e4c89a3c1d
Gitweb:        https://git.kernel.org/tip/1dbb6b1495d472806fef1f4c94f5b3e4c89a3c1d
Author:        David Kaplan <david.kaplan@....com>
AuthorDate:    Wed, 04 Sep 2024 10:07:11 -05:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Thu, 05 Sep 2024 11:20:50 +02:00

x86/bugs: Fix handling when SRSO mitigation is disabled

When the SRSO mitigation is disabled, either via mitigations=off or
spec_rstack_overflow=off, the warning about the lack of IBPB-enhancing
microcode is printed anyway.

This is unnecessary since the user has turned off the mitigation.

  [ bp: Massage, drop SBPB rationale as it doesn't matter because when
    mitigations are disabled x86_pred_cmd is not being used anyway. ]

Signed-off-by: David Kaplan <david.kaplan@....com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
Link: https://lore.kernel.org/r/20240904150711.193022-1-david.kaplan@amd.com
---
 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 189840d..d191542 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: