linux-kernel - [RFC PATCH 06/34] x86/bugs: Restructure rfds mitigation

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Message-ID: <20240912190857.235849-7-david.kaplan@amd.com>
Date: Thu, 12 Sep 2024 14:08:29 -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 06/34] x86/bugs: Restructure rfds mitigation

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

Signed-off-by: David Kaplan <david.kaplan@....com>
---
 arch/x86/kernel/cpu/bugs.c | 38 +++++++++++++++++++++++++++++++-------
 1 file changed, 31 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 0b93a0f030b7..d3e6ce7238e4 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -70,6 +70,9 @@ static void __init taa_apply_mitigation(void);
 static void __init mmio_select_mitigation(void);
 static void __init mmio_update_mitigation(void);
 static void __init mmio_apply_mitigation(void);
+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 l1d_flush_select_mitigation(void);
 static void __init srso_select_mitigation(void);
@@ -193,6 +196,7 @@ void __init cpu_select_mitigations(void)
 	mds_select_mitigation();
 	taa_select_mitigation();
 	mmio_select_mitigation();
+	rfds_select_mitigation();
 	md_clear_select_mitigation();
 	srbds_select_mitigation();
 	l1d_flush_select_mitigation();
@@ -211,10 +215,12 @@ void __init cpu_select_mitigations(void)
 	mds_update_mitigation();
 	taa_update_mitigation();
 	mmio_update_mitigation();
+	rfds_update_mitigation();
 
 	mds_apply_mitigation();
 	taa_apply_mitigation();
 	mmio_apply_mitigation();
+	rfds_apply_mitigation();
 }
 
 /*
@@ -595,9 +601,6 @@ static int __init mmio_stale_data_parse_cmdline(char *str)
 }
 early_param("mmio_stale_data", mmio_stale_data_parse_cmdline);
 
-#undef pr_fmt
-#define pr_fmt(fmt)	"Register File Data Sampling: " fmt
-
 static const char * const rfds_strings[] = {
 	[RFDS_MITIGATION_OFF]			= "Vulnerable",
 	[RFDS_MITIGATION_VERW]			= "Mitigation: Clear Register File",
@@ -613,12 +616,34 @@ static void __init rfds_select_mitigation(void)
 	if (rfds_mitigation == RFDS_MITIGATION_OFF)
 		return;
 
-	if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
-		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
-	else
+	if (rfds_mitigation == RFDS_MITIGATION_AUTO)
+		rfds_mitigation = RFDS_MITIGATION_VERW;
+
+	if (!(x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR))
 		rfds_mitigation = RFDS_MITIGATION_UCODE_NEEDED;
 }
 
+static void __init rfds_update_mitigation(void)
+{
+	if (!boot_cpu_has_bug(X86_BUG_RFDS))
+		return;
+
+	if (mds_mitigation != MDS_MITIGATION_OFF ||
+	    taa_mitigation != TAA_MITIGATION_OFF ||
+	    mmio_mitigation != MMIO_MITIGATION_OFF)
+		rfds_mitigation = RFDS_MITIGATION_VERW;
+
+	pr_info("Register File Data Sampling: %s\n", rfds_strings[rfds_mitigation]);
+}
+
+static void __init rfds_apply_mitigation(void)
+{
+	if (rfds_mitigation == RFDS_MITIGATION_VERW) {
+		if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
+			setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
+	}
+}
+
 static __init int rfds_parse_cmdline(char *str)
 {
 	if (!str)
@@ -689,7 +714,6 @@ static void __init md_clear_update_mitigation(void)
 
 static void __init md_clear_select_mitigation(void)
 {
-	rfds_select_mitigation();
 
 	/*
 	 * As these mitigations are inter-related and rely on VERW instruction
-- 
2.34.1