diff --git a/xen/arch/x86/oprofile/nmi_int.c b/xen/arch/x86/oprofile/nmi_int.c
index 24a1fea86e..b51f17993d 100644
--- a/xen/arch/x86/oprofile/nmi_int.c
+++ b/xen/arch/x86/oprofile/nmi_int.c
@@ -269,8 +269,12 @@ static int __init p4_init(char * cpu_type)
 { 
 	__u8 cpu_model = current_cpu_data.x86_model;
 
-	if ((cpu_model > 6) || (cpu_model == 5))
+	if ((cpu_model > 6) || (cpu_model == 5)) {
+		printk("xenoprof: Initialization failed. "
+		       "Intel processor model %d for pentium 4 family is not "
+		       "supported\n", cpu_model);
 		return 0;
+	}
 
 #ifndef CONFIG_SMP
 	strncpy (cpu_type, "i386/p4", XENOPROF_CPU_TYPE_SIZE - 1);
@@ -301,8 +305,12 @@ static int __init ppro_init(char *cpu_type)
 {
 	__u8 cpu_model = current_cpu_data.x86_model;
 
-	if (cpu_model > 0xd)
+	if (cpu_model > 0xd) {
+		printk("xenoprof: Initialization failed. "
+		       "Intel processor model %d for P6 class family is not "
+		       "supported\n", cpu_model);
 		return 0;
+	}
 
 	if (cpu_model == 9) {
 		strncpy (cpu_type, "i386/p6_mobile", XENOPROF_CPU_TYPE_SIZE - 1);
@@ -324,8 +332,10 @@ int nmi_init(int *num_events, int *is_primary, char *cpu_type)
 	__u8 family = current_cpu_data.x86;
 	int prim = 0;
  
-	if (!cpu_has_apic)
+	if (!cpu_has_apic) {
+		printk("xenoprof: Initialization failed. No apic.\n");
 		return -ENODEV;
+	}
 
 	if (primary_profiler == NULL) {
 		/* For now, only dom0 can be the primary profiler */
@@ -344,6 +354,9 @@ int nmi_init(int *num_events, int *is_primary, char *cpu_type)
 
 			switch (family) {
 			default:
+				printk("xenoprof: Initialization failed. "
+				       "AMD processor family %d is not "
+				       "supported\n", family);
 				return -ENODEV;
 			case 6:
 				model = &op_athlon_spec;
@@ -375,11 +388,17 @@ int nmi_init(int *num_events, int *is_primary, char *cpu_type)
 					break;
 
 				default:
+				printk("xenoprof: Initialization failed. "
+				       "Intel processor family %d is not "
+				       "supported\n", family);
 					return -ENODEV;
 			}
 			break;
 
 		default:
+			printk("xenoprof: Initialization failed. "
+			       "Unsupported processor. Unknown vendor %d\n",
+				vendor);
 			return -ENODEV;
 	}
 
diff --git a/xen/arch/x86/oprofile/xenoprof.c b/xen/arch/x86/oprofile/xenoprof.c
index 479d9c5060..4379d1223b 100644
--- a/xen/arch/x86/oprofile/xenoprof.c
+++ b/xen/arch/x86/oprofile/xenoprof.c
@@ -492,19 +492,23 @@ int xenoprof_op_get_buffer(XEN_GUEST_HANDLE(void) arg)
     return 0;
 }
 
-#define PRIV_OP(op) ( (op == XENOPROF_set_active)       \
-                   || (op == XENOPROF_reserve_counters) \
-                   || (op == XENOPROF_setup_events)     \
-                   || (op == XENOPROF_start)            \
-                   || (op == XENOPROF_stop)             \
-                   || (op == XENOPROF_release_counters) \
-                   || (op == XENOPROF_shutdown))
-
+#define NONPRIV_OP(op) ( (op == XENOPROF_init)          \
+                      || (op == XENOPROF_enable_virq)   \
+                      || (op == XENOPROF_disable_virq)  \
+                      || (op == XENOPROF_get_buffer))
+ 
 int do_xenoprof_op(int op, XEN_GUEST_HANDLE(void) arg)
 {
     int ret = 0;
+    
+    if ( (op < 0) || (op>XENOPROF_last_op) )
+    {
+        printk("xenoprof: invalid operation %d for domain %d\n",
+               op, current->domain->domain_id);
+        return -EINVAL;
+    }
 
-    if ( PRIV_OP(op) && (current->domain != primary_profiler) )
+    if ( !NONPRIV_OP(op) && (current->domain != primary_profiler) )
     {
         printk("xenoprof: dom %d denied privileged operation %d\n",
                current->domain->domain_id, op);