powerpc/64s: Enhance the information in cpu_show_meltdown()

CVE-2018-3639 (powerpc)

Now that we have the security feature flags we can make the
information displayed in the "meltdown" file more informative.

(cherry picked from commit ff348355)
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>

arch/powerpc/include/asm/security_features.h

@@ -10,6 +10,7 @@
 
 
 extern unsigned long powerpc_security_features;
+extern bool rfi_flush;
 
 static inline void security_ftr_set(unsigned long feature)
 {

arch/powerpc/kernel/security.c

@@ -6,6 +6,7 @@
 
 #include <linux/kernel.h>
 #include <linux/device.h>
+#include <linux/seq_buf.h>
 
 #include <asm/security_features.h>
 
@@ -19,8 +20,33 @@ unsigned long powerpc_security_features __read_mostly = \
 
 ssize_t cpu_show_meltdown(struct device *dev, struct device_attribute *attr, char *buf)
 {
+	bool thread_priv;
+
+	thread_priv = security_ftr_enabled(SEC_FTR_L1D_THREAD_PRIV);
+
+	if (rfi_flush || thread_priv) {
+		struct seq_buf s;
+		seq_buf_init(&s, buf, PAGE_SIZE - 1);
+
+		seq_buf_printf(&s, "Mitigation: ");
+
 		if (rfi_flush)
-		return sprintf(buf, "Mitigation: RFI Flush\n");
+			seq_buf_printf(&s, "RFI Flush");
+
+		if (rfi_flush && thread_priv)
+			seq_buf_printf(&s, ", ");
+
+		if (thread_priv)
+			seq_buf_printf(&s, "L1D private per thread");
+
+		seq_buf_printf(&s, "\n");
+
+		return s.len;
+	}
+
+	if (!security_ftr_enabled(SEC_FTR_L1D_FLUSH_HV) &&
+	    !security_ftr_enabled(SEC_FTR_L1D_FLUSH_PR))
+		return sprintf(buf, "Not affected\n");
 
 	return sprintf(buf, "Vulnerable\n");
 }