linux-kernel - [PATCH v4 06/36] x86/bugs: Restructure srbds mitigation

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Message-ID: <20250310164023.779191-7-david.kaplan@amd.com>
Date: Mon, 10 Mar 2025 11:39:53 -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: <linux-kernel@...r.kernel.org>, Brendan Jackman <jackmanb@...gle.com>,
	Derek Manwaring <derekmn@...zon.com>
Subject: [PATCH v4 06/36] x86/bugs: Restructure srbds mitigation

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

Define new AUTO mitigation for SRBDS.

Signed-off-by: David Kaplan <david.kaplan@....com>
---
 arch/x86/kernel/cpu/bugs.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 841ab123a180..fd04de518fd0 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -72,6 +72,7 @@ static void __init rfds_select_mitigation(void);
 static void __init rfds_update_mitigation(void);
 static void __init rfds_apply_mitigation(void);
 static void __init srbds_select_mitigation(void);
+static void __init srbds_apply_mitigation(void);
 static void __init l1d_flush_select_mitigation(void);
 static void __init srso_select_mitigation(void);
 static void __init gds_select_mitigation(void);
@@ -222,6 +223,7 @@ void __init cpu_select_mitigations(void)
 	taa_apply_mitigation();
 	mmio_apply_mitigation();
 	rfds_apply_mitigation();
+	srbds_apply_mitigation();
 }
 
 /*
@@ -680,6 +682,7 @@ early_param("reg_file_data_sampling", rfds_parse_cmdline);
 
 enum srbds_mitigations {
 	SRBDS_MITIGATION_OFF,
+	SRBDS_MITIGATION_AUTO,
 	SRBDS_MITIGATION_UCODE_NEEDED,
 	SRBDS_MITIGATION_FULL,
 	SRBDS_MITIGATION_TSX_OFF,
@@ -687,7 +690,7 @@ enum srbds_mitigations {
 };
 
 static enum srbds_mitigations srbds_mitigation __ro_after_init =
-	IS_ENABLED(CONFIG_MITIGATION_SRBDS) ? SRBDS_MITIGATION_FULL : SRBDS_MITIGATION_OFF;
+	IS_ENABLED(CONFIG_MITIGATION_SRBDS) ? SRBDS_MITIGATION_AUTO : SRBDS_MITIGATION_OFF;
 
 static const char * const srbds_strings[] = {
 	[SRBDS_MITIGATION_OFF]		= "Vulnerable",
@@ -738,8 +741,13 @@ void update_srbds_msr(void)
 
 static void __init srbds_select_mitigation(void)
 {
-	if (!boot_cpu_has_bug(X86_BUG_SRBDS))
+	if (!boot_cpu_has_bug(X86_BUG_SRBDS) || cpu_mitigations_off()) {
+		srbds_mitigation = SRBDS_MITIGATION_OFF;
 		return;
+	}
+
+	if (srbds_mitigation == SRBDS_MITIGATION_AUTO)
+		srbds_mitigation = SRBDS_MITIGATION_FULL;
 
 	/*
 	 * Check to see if this is one of the MDS_NO systems supporting TSX that
@@ -753,13 +761,17 @@ static void __init srbds_select_mitigation(void)
 		srbds_mitigation = SRBDS_MITIGATION_HYPERVISOR;
 	else if (!boot_cpu_has(X86_FEATURE_SRBDS_CTRL))
 		srbds_mitigation = SRBDS_MITIGATION_UCODE_NEEDED;
-	else if (cpu_mitigations_off() || srbds_off)
+	else if (srbds_off)
 		srbds_mitigation = SRBDS_MITIGATION_OFF;
 
-	update_srbds_msr();
 	pr_info("%s\n", srbds_strings[srbds_mitigation]);
 }
 
+static void __init srbds_apply_mitigation(void)
+{
+	update_srbds_msr();
+}
+
 static int __init srbds_parse_cmdline(char *str)
 {
 	if (!str)
-- 
2.34.1