linux-kernel - [RFC PATCH 09/34] x86/bugs: Restructure gds mitigation

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Message-ID: <20240912190857.235849-10-david.kaplan@amd.com>
Date: Thu, 12 Sep 2024 14:08:32 -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>
Subject: [RFC PATCH 09/34] x86/bugs: Restructure gds mitigation

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

Define new AUTO mitigation for gds.

Signed-off-by: David Kaplan <david.kaplan@....com>
---
 arch/x86/kernel/cpu/bugs.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0fb97b94f5b9..7fee5c3de135 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -76,6 +76,7 @@ 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);
+static void __init gds_apply_mitigation(void);
 
 /* The base value of the SPEC_CTRL MSR without task-specific bits set */
 u64 x86_spec_ctrl_base;
@@ -220,6 +221,7 @@ void __init cpu_select_mitigations(void)
 	mmio_apply_mitigation();
 	rfds_apply_mitigation();
 	srbds_apply_mitigation();
+	gds_apply_mitigation();
 }
 
 /*
@@ -801,6 +803,7 @@ early_param("l1d_flush", l1d_flush_parse_cmdline);
 
 enum gds_mitigations {
 	GDS_MITIGATION_OFF,
+	GDS_MITIGATION_AUTO,
 	GDS_MITIGATION_UCODE_NEEDED,
 	GDS_MITIGATION_FORCE,
 	GDS_MITIGATION_FULL,
@@ -809,7 +812,7 @@ enum gds_mitigations {
 };
 
 static enum gds_mitigations gds_mitigation __ro_after_init =
-	IS_ENABLED(CONFIG_MITIGATION_GDS) ? GDS_MITIGATION_FULL : GDS_MITIGATION_OFF;
+	IS_ENABLED(CONFIG_MITIGATION_GDS) ? GDS_MITIGATION_AUTO : GDS_MITIGATION_OFF;
 
 static const char * const gds_strings[] = {
 	[GDS_MITIGATION_OFF]		= "Vulnerable",
@@ -850,6 +853,7 @@ void update_gds_msr(void)
 	case GDS_MITIGATION_FORCE:
 	case GDS_MITIGATION_UCODE_NEEDED:
 	case GDS_MITIGATION_HYPERVISOR:
+	case GDS_MITIGATION_AUTO:
 		return;
 	}
 
@@ -873,13 +877,16 @@ static void __init gds_select_mitigation(void)
 
 	if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
 		gds_mitigation = GDS_MITIGATION_HYPERVISOR;
-		goto out;
+		return;
 	}
 
 	if (cpu_mitigations_off())
 		gds_mitigation = GDS_MITIGATION_OFF;
 	/* Will verify below that mitigation _can_ be disabled */
 
+	if (gds_mitigation == GDS_MITIGATION_AUTO)
+		gds_mitigation = GDS_MITIGATION_FULL;
+
 	/* No microcode */
 	if (!(x86_arch_cap_msr & ARCH_CAP_GDS_CTRL)) {
 		if (gds_mitigation == GDS_MITIGATION_FORCE) {
@@ -892,7 +899,7 @@ static void __init gds_select_mitigation(void)
 		} else {
 			gds_mitigation = GDS_MITIGATION_UCODE_NEEDED;
 		}
-		goto out;
+		return;
 	}
 
 	/* Microcode has mitigation, use it */
@@ -914,8 +921,14 @@ static void __init gds_select_mitigation(void)
 		gds_mitigation = GDS_MITIGATION_FULL_LOCKED;
 	}
 
+}
+
+static void __init gds_apply_mitigation(void)
+{
+	if (!boot_cpu_has_bug(X86_BUG_GDS))
+		return;
+
 	update_gds_msr();
-out:
 	pr_info("%s\n", gds_strings[gds_mitigation]);
 }
 
-- 
2.34.1