linux-kernel - [RFC PATCH 15/56] x86/bugs: Reset BHI mitigations

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Message-ID: <20251013143444.3999-16-david.kaplan@amd.com>
Date: Mon, 13 Oct 2025 09:34:03 -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: Alexander Graf <graf@...zon.com>, Boris Ostrovsky
	<boris.ostrovsky@...cle.com>, <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH 15/56] x86/bugs: Reset BHI mitigations

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

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

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index e765ac0b9240..67561e5c2154 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2360,6 +2360,17 @@ static void __init bhi_apply_mitigation(void)
 	setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_VMEXIT);
 }
 
+#ifdef CONFIG_DYNAMIC_MITIGATIONS
+static void bhi_reset_mitigation(void)
+{
+	/* RRSBA already cleared in spectre_v2_reset_mitigation() */
+	setup_clear_cpu_cap(X86_FEATURE_CLEAR_BHB_VMEXIT);
+	setup_clear_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP);
+	bhi_mitigation = IS_ENABLED(CONFIG_MITIGATION_SPECTRE_BHI) ?
+		BHI_MITIGATION_AUTO : BHI_MITIGATION_OFF;
+}
+#endif
+
 static void __init spectre_v2_select_mitigation(void)
 {
 	if ((spectre_v2_cmd == SPECTRE_V2_CMD_RETPOLINE ||
@@ -3954,5 +3965,6 @@ void arch_cpu_reset_mitigations(void)
 	srbds_reset_mitigation();
 	srso_reset_mitigation();
 	gds_reset_mitigation();
+	bhi_reset_mitigation();
 }
 #endif
-- 
2.34.1