linux-kernel - [tip: x86/bugs] x86/bugs: Restructure L1TF mitigation

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Message-ID: <174618199974.22196.12832189173399649709.tip-bot2@tip-bot2>
Date: Fri, 02 May 2025 10:33:19 -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: Restructure L1TF mitigation

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

Commit-ID:     d43ba2dc8eeeca21811fd9b30e3bd15bb35caaec
Gitweb:        https://git.kernel.org/tip/d43ba2dc8eeeca21811fd9b30e3bd15bb35caaec
Author:        David Kaplan <david.kaplan@....com>
AuthorDate:    Fri, 18 Apr 2025 11:17:20 -05:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Tue, 29 Apr 2025 18:57:30 +02:00

x86/bugs: Restructure L1TF mitigation

Restructure L1TF to use select/apply functions to create consistent
vulnerability handling.

Define new AUTO mitigation for L1TF.

Signed-off-by: David Kaplan <david.kaplan@....com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@...nel.org>
Link: https://lore.kernel.org/20250418161721.1855190-16-david.kaplan@amd.com
---
 arch/x86/include/asm/processor.h |  1 +
 arch/x86/kernel/cpu/bugs.c       | 25 +++++++++++++++++++------
 arch/x86/kvm/vmx/vmx.c           |  2 ++
 3 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 5d2f7e5..0973bed 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -734,6 +734,7 @@ void store_cpu_caps(struct cpuinfo_x86 *info);
 
 enum l1tf_mitigations {
 	L1TF_MITIGATION_OFF,
+	L1TF_MITIGATION_AUTO,
 	L1TF_MITIGATION_FLUSH_NOWARN,
 	L1TF_MITIGATION_FLUSH,
 	L1TF_MITIGATION_FLUSH_NOSMT,
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index fbb4f13..25d84e2 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -67,6 +67,7 @@ static void __init spectre_v2_user_apply_mitigation(void);
 static void __init ssb_select_mitigation(void);
 static void __init ssb_apply_mitigation(void);
 static void __init l1tf_select_mitigation(void);
+static void __init l1tf_apply_mitigation(void);
 static void __init mds_select_mitigation(void);
 static void __init mds_update_mitigation(void);
 static void __init mds_apply_mitigation(void);
@@ -245,6 +246,7 @@ void __init cpu_select_mitigations(void)
 	retbleed_apply_mitigation();
 	spectre_v2_user_apply_mitigation();
 	ssb_apply_mitigation();
+	l1tf_apply_mitigation();
 	mds_apply_mitigation();
 	taa_apply_mitigation();
 	mmio_apply_mitigation();
@@ -2538,7 +2540,7 @@ EXPORT_SYMBOL_GPL(itlb_multihit_kvm_mitigation);
 
 /* Default mitigation for L1TF-affected CPUs */
 enum l1tf_mitigations l1tf_mitigation __ro_after_init =
-	IS_ENABLED(CONFIG_MITIGATION_L1TF) ? L1TF_MITIGATION_FLUSH : L1TF_MITIGATION_OFF;
+	IS_ENABLED(CONFIG_MITIGATION_L1TF) ? L1TF_MITIGATION_AUTO : L1TF_MITIGATION_OFF;
 #if IS_ENABLED(CONFIG_KVM_INTEL)
 EXPORT_SYMBOL_GPL(l1tf_mitigation);
 #endif
@@ -2586,22 +2588,33 @@ 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()) {
+		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;
+	}
+}
+
+static void __init l1tf_apply_mitigation(void)
+{
 	u64 half_pa;
 
 	if (!boot_cpu_has_bug(X86_BUG_L1TF))
 		return;
 
-	if (cpu_mitigations_off())
-		l1tf_mitigation = L1TF_MITIGATION_OFF;
-	else if (cpu_mitigations_auto_nosmt())
-		l1tf_mitigation = L1TF_MITIGATION_FLUSH_NOSMT;
-
 	override_cache_bits(&boot_cpu_data);
 
 	switch (l1tf_mitigation) {
 	case L1TF_MITIGATION_OFF:
 	case L1TF_MITIGATION_FLUSH_NOWARN:
 	case L1TF_MITIGATION_FLUSH:
+	case L1TF_MITIGATION_AUTO:
 		break;
 	case L1TF_MITIGATION_FLUSH_NOSMT:
 	case L1TF_MITIGATION_FULL:
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a1754f7..0aba471 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -273,6 +273,7 @@ static int vmx_setup_l1d_flush(enum vmx_l1d_flush_state l1tf)
 		case L1TF_MITIGATION_OFF:
 			l1tf = VMENTER_L1D_FLUSH_NEVER;
 			break;
+		case L1TF_MITIGATION_AUTO:
 		case L1TF_MITIGATION_FLUSH_NOWARN:
 		case L1TF_MITIGATION_FLUSH:
 		case L1TF_MITIGATION_FLUSH_NOSMT:
@@ -7704,6 +7705,7 @@ int vmx_vm_init(struct kvm *kvm)
 		case L1TF_MITIGATION_FLUSH_NOWARN:
 			/* 'I explicitly don't care' is set */
 			break;
+		case L1TF_MITIGATION_AUTO:
 		case L1TF_MITIGATION_FLUSH:
 		case L1TF_MITIGATION_FLUSH_NOSMT:
 		case L1TF_MITIGATION_FULL: