[tip: x86/bugs] x86/bugs: Restructure SRBDS mitigation

["tip-bot2 for David Kaplan" <tip-bot2@linutronix.de>]

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

Commit-ID:     2178ac58e176d8e1e4529b02647f5e549bb88405
Gitweb:        https://git.kernel.org/tip/2178ac58e176d8e1e4529b02647f5e549bb88405
Author:        David Kaplan <david.kaplan@amd.com>
AuthorDate:    Fri, 18 Apr 2025 11:17:11 -05:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Mon, 28 Apr 2025 15:05:41 +02:00

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@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/20250418161721.1855190-7-david.kaplan@amd.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 98476b8..25b74a7 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);
@@ -225,6 +226,7 @@ void __init cpu_select_mitigations(void)
 	taa_apply_mitigation();
 	mmio_apply_mitigation();
 	rfds_apply_mitigation();
+	srbds_apply_mitigation();
 }
 
 /*
@@ -693,6 +695,7 @@ 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,
@@ -700,7 +703,7 @@ 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",
@@ -751,8 +754,13 @@ 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
@@ -766,13 +774,17 @@ 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)