[RFC PATCH 06/56] x86/bugs: Reset retbleed mitigations

David Kaplan
2025-10-13T14:35:26Z

Add function to reset retbleed mitigations back to their boot-time
defaults.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
arch/x86/kernel/cpu/bugs.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0430635bb17d..1f56ccb5f641 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1542,6 +1542,20 @@ static void __init retbleed_apply_mitigation(void)
cpu_smt_disable(false);
}

+#ifdef CONFIG_DYNAMIC_MITIGATIONS
+static void retbleed_reset_mitigation(void)
+{
+ setup_clear_cpu_cap(X86_FEATURE_RETHUNK);
+ setup_clear_cpu_cap(X86_FEATURE_UNRET);
+ setup_clear_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+ setup_clear_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
+ setup_clear_cpu_cap(X86_FEATURE_CALL_DEPTH);
+ x86_return_thunk = __x86_return_thunk;
+ retbleed_mitigation = IS_ENABLED(CONFIG_MITIGATION_RETBLEED) ?
+ RETBLEED_MITIGATION_AUTO : RETBLEED_MITIGATION_NONE;
+}
+#endif
+
#undef pr_fmt
#define pr_fmt(fmt) "ITS: " fmt

@@ -3829,5 +3843,6 @@ void arch_cpu_reset_mitigations(void)
{
spectre_v1_reset_mitigation();
spectre_v2_reset_mitigation();
+ retbleed_reset_mitigation();
}
#endif
--
2.34.1