Use attack vector controls to determine if taa mitigation is required.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
 arch/x86/kernel/cpu/bugs.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 298acb80d126..af5aaa0397c7 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -572,8 +572,12 @@ static void __init taa_select_mitigation(void)
 		return;
 
 	/* Microcode will be checked in taa_update_mitigation(). */
-	if (taa_mitigation == TAA_MITIGATION_AUTO)
-		taa_mitigation = TAA_MITIGATION_VERW;
+	if (taa_mitigation == TAA_MITIGATION_AUTO) {
+		if (should_mitigate_vuln(X86_BUG_TAA))
+			taa_mitigation = TAA_MITIGATION_VERW;
+		else
+			taa_mitigation = TAA_MITIGATION_OFF;
+	}
 
 }
 
@@ -620,7 +624,8 @@ static void __init taa_apply_mitigation(void)
 		 */
 		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
 
-		if (taa_nosmt || cpu_mitigations_auto_nosmt())
+		if (taa_nosmt || cpu_mitigations_auto_nosmt() ||
+		    cpu_mitigate_attack_vector(CPU_MITIGATE_CROSS_THREAD))
 			cpu_smt_disable(false);
 	}
 
-- 
2.34.1

On Wed, Jan 08, 2025 at 02:25:03PM -0600, David Kaplan wrote:
> @@ -620,7 +624,8 @@ static void __init taa_apply_mitigation(void)
>  		 */
>  		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
>  
> -		if (taa_nosmt || cpu_mitigations_auto_nosmt())
> +		if (taa_nosmt || cpu_mitigations_auto_nosmt() ||
> +		    cpu_mitigate_attack_vector(CPU_MITIGATE_CROSS_THREAD))
>  			cpu_smt_disable(false);

There's a huge overlap between cpu_mitigations_auto_nosmt() and
CPU_MITIGATE_CROSS_THREAD.

IIUC, the main difference is that cpu_mitigations_auto_nosmt() selects
all the vectors whereas mitigate_cross_thread=on can be combined with
individual vectors.

Maybe we need a should_disable_smt() helper which checks both?

-- 
Josh