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

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 98476b8ba4fd3500f88842bcad741eaa1a07204b..25b74a78caa37ebc57797b1357d1fc24cbf356b0 100644 (file)
--- 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)