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 | 33 ++++++++++++++++++++++++++-------
 1 file changed, 26 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index a8da097ab2d5..871b9f93b714 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();
 }
 
 /*
@@ -607,9 +613,6 @@ 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",
@@ -627,11 +630,28 @@ static void __init rfds_select_mitigation(void)
 
 	if (rfds_mitigation == RFDS_MITIGATION_AUTO)
 		rfds_mitigation = RFDS_MITIGATION_VERW;
+}
 
-	if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
+static void __init rfds_update_mitigation(void)
+{
+	if (!boot_cpu_has_bug(X86_BUG_RFDS) || cpu_mitigations_off())
+		return;
+
+	if (verw_mitigation_enabled())
+		rfds_mitigation = RFDS_MITIGATION_VERW;
+
+	if (rfds_mitigation == RFDS_MITIGATION_VERW) {
+		if (!(x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR))
+			rfds_mitigation = RFDS_MITIGATION_UCODE_NEEDED;
+	}
+
+	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)
 		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
-	else
-		rfds_mitigation = RFDS_MITIGATION_UCODE_NEEDED;
 }
 
 static __init int rfds_parse_cmdline(char *str)
@@ -704,7 +724,6 @@ 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 Wed, Jan 08, 2025 at 02:24:47PM -0600, David Kaplan wrote:
> @@ -627,11 +630,28 @@ static void __init rfds_select_mitigation(void)
>  
>  	if (rfds_mitigation == RFDS_MITIGATION_AUTO)
>  		rfds_mitigation = RFDS_MITIGATION_VERW;

Another superfluous return above this one.

> +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;

Hm, unlike the other VERW mitigations, this doesn't even attempt to do
VERW on missing ucode.

Ah well, it was already like that and I doubt anybody cares at this
point.

-- 
Josh