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

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
 arch/x86/kernel/cpu/bugs.c | 40 ++++++++++++++++++++++++++++++++------
 1 file changed, 34 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index a727f7998bec..de431f2bb012 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);
@@ -197,6 +200,7 @@ 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();
@@ -215,10 +219,12 @@ 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();
 }
 
 /*
@@ -614,22 +620,45 @@ static const char * const rfds_strings[] = {
 	[RFDS_MITIGATION_UCODE_NEEDED]		= "Vulnerable: No microcode",
 };
 
+static bool __init rfds_has_ucode(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_OFF)
-		return;
 
 	if (rfds_mitigation == RFDS_MITIGATION_AUTO)
 		rfds_mitigation = RFDS_MITIGATION_VERW;
 
-	if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
+	if (rfds_has_ucode())
+		verw_mitigation_selected = true;
+}
+
+static void __init rfds_update_mitigation(void)
+{
+	if (!boot_cpu_has_bug(X86_BUG_RFDS) || cpu_mitigations_off())
+		return;
+
+	if (verw_mitigation_selected)
+		rfds_mitigation = RFDS_MITIGATION_VERW;
+
+	if (rfds_mitigation == RFDS_MITIGATION_VERW) {
+		if (!rfds_has_ucode())
+			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)
@@ -702,7 +731,6 @@ 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

On Mon, Mar 10, 2025 at 11:39:51AM -0500, David Kaplan wrote:
>  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_OFF)
> -		return;

The removal of this RFDS_MITIGATION_OFF check can cause
verw_mitigation_selected to get wrongly enabled below if it was
RFDS_MITIGATION_OFF to begin with.

I think it's only a bisection issue, that gets re-added later with
"x86/bugs: Add attack vector controls for rfds".

>  
>  	if (rfds_mitigation == RFDS_MITIGATION_AUTO)
>  		rfds_mitigation = RFDS_MITIGATION_VERW;
>  
> -	if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
> +	if (rfds_has_ucode())
> +		verw_mitigation_selected = true;
> +}

-- 
Josh