linux-kernel - [PATCH v5 16/20] x86/bugs: Add attack vector controls for L1TF

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Message-ID: <20250509162839.3057217-17-david.kaplan@amd.com>
Date: Fri, 9 May 2025 11:28:35 -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 v5 16/20] x86/bugs: Add attack vector controls for L1TF

Use attack vector controls to determine if L1TF mitigation is required.

Disable SMT if cross-thread protection is desired.

Signed-off-by: David Kaplan <david.kaplan@....com>
---
 arch/x86/kernel/cpu/bugs.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 6a4bc80be1e9..19a176369b22 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2697,17 +2697,23 @@ static void override_cache_bits(struct cpuinfo_x86 *c)
 
 static void __init l1tf_select_mitigation(void)
 {
-	if (!boot_cpu_has_bug(X86_BUG_L1TF) || cpu_mitigations_off()) {
+	if (!boot_cpu_has_bug(X86_BUG_L1TF)) {
 		l1tf_mitigation = L1TF_MITIGATION_OFF;
 		return;
 	}
 
-	if (l1tf_mitigation == L1TF_MITIGATION_AUTO) {
-		if (cpu_mitigations_auto_nosmt())
-			l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;
-		else
-			l1tf_mitigation = L1TF_MITIGATION_FLUSH;
+	if (l1tf_mitigation != L1TF_MITIGATION_AUTO)
+		return;
+
+	if (!should_mitigate_vuln(X86_BUG_L1TF)) {
+		l1tf_mitigation = L1TF_MITIGATION_OFF;
+		return;
 	}
+
+	if (smt_mitigations == SMT_MITIGATIONS_ON)
+		l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;
+	else
+		l1tf_mitigation = L1TF_MITIGATION_FLUSH;
 }
 
 static void __init l1tf_apply_mitigation(void)
-- 
2.34.1