x86/bugs: Add attack vector controls for SRBDS

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

Signed-off-by: David Kaplan <[email protected]>
Signed-off-by: Borislav Petkov (AMD) <[email protected]>
Link: https://lore.kernel.org/[email protected]

Author: dkaplan2

arch/x86/kernel/cpu/bugs.c

@@ -870,13 +870,19 @@ void update_srbds_msr(void)
 
 static void __init srbds_select_mitigation(void)
 {
-	if (!boot_cpu_has_bug(X86_BUG_SRBDS) || cpu_mitigations_off()) {
+	if (!boot_cpu_has_bug(X86_BUG_SRBDS)) {
 		srbds_mitigation = SRBDS_MITIGATION_OFF;
 		return;
 	}
 
-	if (srbds_mitigation == SRBDS_MITIGATION_AUTO)
-		srbds_mitigation = SRBDS_MITIGATION_FULL;
+	if (srbds_mitigation == SRBDS_MITIGATION_AUTO) {
+		if (should_mitigate_vuln(X86_BUG_SRBDS))
+			srbds_mitigation = SRBDS_MITIGATION_FULL;
+		else {
+			srbds_mitigation = SRBDS_MITIGATION_OFF;
+			return;
+		}
+	}
 
 	/*
 	 * Check to see if this is one of the MDS_NO systems supporting TSX that