linux-kernel - [tip: x86/bugs] x86/bugs: Restructure RFDS mitigation

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Message-ID: <174618201173.22196.6101974953788091518.tip-bot2@tip-bot2>
Date: Fri, 02 May 2025 10:33:31 -0000
From: "tip-bot2 for David Kaplan" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: David Kaplan <david.kaplan@....com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, Josh Poimboeuf <jpoimboe@...nel.org>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/bugs] x86/bugs: Restructure RFDS mitigation

The following commit has been merged into the x86/bugs branch of tip:

Commit-ID:     203d81f8e167a9e82747a14dace40e0abbd5c791
Gitweb:        https://git.kernel.org/tip/203d81f8e167a9e82747a14dace40e0abbd5c791
Author:        David Kaplan <david.kaplan@....com>
AuthorDate:    Fri, 18 Apr 2025 11:17:09 -05:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Mon, 28 Apr 2025 13:46:11 +02:00

x86/bugs: Restructure RFDS mitigation

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

  [ bp: Rename the oneline helper to what it checks. ]

Signed-off-by: David Kaplan <david.kaplan@....com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@...nel.org>
Link: https://lore.kernel.org/20250418161721.1855190-5-david.kaplan@amd.com
---
 arch/x86/kernel/cpu/bugs.c | 41 ++++++++++++++++++++++++++++++++-----
 1 file changed, 36 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index bc74c22..2705105 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);
@@ -200,6 +203,7 @@ 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();
@@ -218,10 +222,12 @@ 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();
 }
 
 /*
@@ -624,22 +630,48 @@ static const char * const rfds_strings[] = {
 	[RFDS_MITIGATION_UCODE_NEEDED]		= "Vulnerable: No microcode",
 };
 
+static inline bool __init verw_clears_cpu_reg_file(void)
+{
+	return (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR);
+}
+
 static void __init rfds_select_mitigation(void)
 {
 	if (!boot_cpu_has_bug(X86_BUG_RFDS) || cpu_mitigations_off()) {
 		rfds_mitigation = RFDS_MITIGATION_OFF;
 		return;
 	}
+
+	if (rfds_mitigation == RFDS_MITIGATION_AUTO)
+		rfds_mitigation = RFDS_MITIGATION_VERW;
+
 	if (rfds_mitigation == RFDS_MITIGATION_OFF)
 		return;
 
-	if (rfds_mitigation == RFDS_MITIGATION_AUTO)
+	if (verw_clears_cpu_reg_file())
+		verw_clear_cpu_buf_mitigation_selected = true;
+}
+
+static void __init rfds_update_mitigation(void)
+{
+	if (!boot_cpu_has_bug(X86_BUG_RFDS) || cpu_mitigations_off())
+		return;
+
+	if (verw_clear_cpu_buf_mitigation_selected)
 		rfds_mitigation = RFDS_MITIGATION_VERW;
 
-	if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
+	if (rfds_mitigation == RFDS_MITIGATION_VERW) {
+		if (!verw_clears_cpu_reg_file())
+			rfds_mitigation = RFDS_MITIGATION_UCODE_NEEDED;
+	}
+
+	pr_info("%s\n", rfds_strings[rfds_mitigation]);
+}
+
+static void __init rfds_apply_mitigation(void)
+{
+	if (rfds_mitigation == RFDS_MITIGATION_VERW)
 		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
-	else
-		rfds_mitigation = RFDS_MITIGATION_UCODE_NEEDED;
 }
 
 static __init int rfds_parse_cmdline(char *str)
@@ -712,7 +744,6 @@ out:
 
 static void __init md_clear_select_mitigation(void)
 {
-	rfds_select_mitigation();
 
 	/*
 	 * As these mitigations are inter-related and rely on VERW instruction