[tip: x86/bugs] x86/bugs: Restructure L1TF mitigation

tip-bot2 for David Kaplan
2025-05-02T10:33:22Z

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@amd.com>
AuthorDate: Fri, 18 Apr 2025 11:17:20 -05:00
Committer: Borislav Petkov (AMD) <bp@alien8.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@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.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: