linux-kernel - [PATCH 1/3] x86/bugs: Add SRSO_MITIGATION

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Message-ID: <20250625155805.600376-2-david.kaplan@amd.com>
Date: Wed, 25 Jun 2025 10:58:03 -0500
From: David Kaplan <david.kaplan@....com>
To: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Ingo Molnar
	<mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
	<x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>
CC: <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/3] x86/bugs: Add SRSO_MITIGATION_NOSMT

Zen1 and Zen2 CPUs with SMT disabled are not vulnerable to SRSO.
Instead of overloading the X86_FEATURE_SRSO_NO bit to indicate this,
define a separate mitigation to make the code cleaner.

Signed-off-by: David Kaplan <david.kaplan@....com>
Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>
---
 arch/x86/kernel/cpu/bugs.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index bdef2c9aa1b8..6c991afb7b78 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2851,6 +2851,7 @@ enum srso_mitigation {
 	SRSO_MITIGATION_UCODE_NEEDED,
 	SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
 	SRSO_MITIGATION_MICROCODE,
+	SRSO_MITIGATION_NOSMT,
 	SRSO_MITIGATION_SAFE_RET,
 	SRSO_MITIGATION_IBPB,
 	SRSO_MITIGATION_IBPB_ON_VMEXIT,
@@ -2862,6 +2863,7 @@ static const char * const srso_strings[] = {
 	[SRSO_MITIGATION_UCODE_NEEDED]		= "Vulnerable: No microcode",
 	[SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED]	= "Vulnerable: Safe RET, no microcode",
 	[SRSO_MITIGATION_MICROCODE]		= "Vulnerable: Microcode, no safe RET",
+	[SRSO_MITIGATION_NOSMT]			= "Mitigation: SMT disabled",
 	[SRSO_MITIGATION_SAFE_RET]		= "Mitigation: Safe RET",
 	[SRSO_MITIGATION_IBPB]			= "Mitigation: IBPB",
 	[SRSO_MITIGATION_IBPB_ON_VMEXIT]	= "Mitigation: IBPB on VMEXIT only",
@@ -2914,8 +2916,7 @@ static void __init srso_select_mitigation(void)
 		 * IBPB microcode has been applied.
 		 */
 		if (boot_cpu_data.x86 < 0x19 && !cpu_smt_possible()) {
-			setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
-			srso_mitigation = SRSO_MITIGATION_NONE;
+			srso_mitigation = SRSO_MITIGATION_NOSMT;
 			return;
 		}
 	} else {
@@ -2968,8 +2969,7 @@ static void __init srso_update_mitigation(void)
 		srso_mitigation = SRSO_MITIGATION_IBPB;
 
 	if (boot_cpu_has_bug(X86_BUG_SRSO) &&
-	    !cpu_mitigations_off() &&
-	    !boot_cpu_has(X86_FEATURE_SRSO_NO))
+	    !cpu_mitigations_off())
 		pr_info("%s\n", srso_strings[srso_mitigation]);
 }
 
@@ -3265,9 +3265,6 @@ static ssize_t retbleed_show_state(char *buf)
 
 static ssize_t srso_show_state(char *buf)
 {
-	if (boot_cpu_has(X86_FEATURE_SRSO_NO))
-		return sysfs_emit(buf, "Mitigation: SMT disabled\n");
-
 	return sysfs_emit(buf, "%s\n", srso_strings[srso_mitigation]);
 }
 
-- 
2.34.1