linux-kernel - [RFC PATCH 22/34] x86/bugs: Add attack vector controls for taa

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Message-ID: <20240912190857.235849-23-david.kaplan@amd.com>
Date: Thu, 12 Sep 2024 14:08:45 -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: [RFC PATCH 22/34] x86/bugs: Add attack vector controls for taa

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

Signed-off-by: David Kaplan <david.kaplan@....com>
---
 arch/x86/kernel/cpu/bugs.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index a5fbd7cc9e25..f042c5595463 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -513,11 +513,17 @@ static void __init taa_select_mitigation(void)
 	if (taa_mitigation == TAA_MITIGATION_OFF)
 		return;
 
-	/* This handles the AUTO case. */
-	if (boot_cpu_has(X86_FEATURE_MD_CLEAR))
-		taa_mitigation = TAA_MITIGATION_VERW;
-	else
-		taa_mitigation = TAA_MITIGATION_UCODE_NEEDED;
+	if (taa_mitigation == TAA_MITIGATION_AUTO) {
+		if (should_mitigate_vuln(TAA)) {
+			if (boot_cpu_has(X86_FEATURE_MD_CLEAR))
+				taa_mitigation = TAA_MITIGATION_VERW;
+			else
+				taa_mitigation = TAA_MITIGATION_UCODE_NEEDED;
+		} else {
+			taa_mitigation = TAA_MITIGATION_OFF;
+			return;
+		}
+	}
 
 	/*
 	 * VERW doesn't clear the CPU buffers when MD_CLEAR=1 and MDS_NO=1.
@@ -560,7 +566,8 @@ static void __init taa_apply_mitigation(void)
 		 */
 		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
 
-		if (taa_nosmt || cpu_mitigations_auto_nosmt())
+		if (taa_nosmt || cpu_mitigations_auto_nosmt() ||
+		    cpu_mitigate_attack_vector(CPU_MITIGATE_CROSS_THREAD))
 			cpu_smt_disable(false);
 	}
 
-- 
2.34.1