linux-kernel - [RFC PATCH 12/56] x86/bugs: Reset SRBDS mitigations

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Message-ID: <20251013143444.3999-13-david.kaplan@amd.com>
Date: Mon, 13 Oct 2025 09:34:00 -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 12/56] x86/bugs: Reset SRBDS mitigations

Add function to reset SRBDS 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 9139c8187913..9a9d5309aa56 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -993,6 +993,17 @@ static void __init srbds_apply_mitigation(void)
 	update_srbds_msr();
 }
 
+#ifdef CONFIG_DYNAMIC_MITIGATIONS
+static void srbds_reset_mitigation(void)
+{
+	/* To cause the MSR bit to be cleared */
+	srbds_mitigation = SRBDS_MITIGATION_FULL;
+	update_srbds_msr();
+	srbds_mitigation = IS_ENABLED(CONFIG_MITIGATION_SRBDS) ?
+		SRBDS_MITIGATION_AUTO : SRBDS_MITIGATION_OFF;
+}
+#endif
+
 static int __init srbds_parse_cmdline(char *str)
 {
 	if (!str)
@@ -3913,5 +3924,6 @@ void arch_cpu_reset_mitigations(void)
 	l1tf_reset_mitigation();
 	mds_reset_mitigation();
 	mmio_reset_mitigation();
+	srbds_reset_mitigation();
 }
 #endif
-- 
2.34.1