oprofile, x86: Add kernel parameter oprofile.cpu_type=timer

We need this to better test x86 NMI timer mode. Otherwise it is very
hard to setup systems with NMI timer enabled, but we have this e.g. in
virtual machine environments.
Signed-off-by: Robert Richter <robert.richter@amd.com>

Documentation/kernel-parameters.txt

@@ -1848,6 +1848,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			arch_perfmon: [X86] Force use of architectural
 				perfmon on Intel CPUs instead of the
 				CPU specific event set.
+			timer: [X86] Force use of architectural NMI
+				timer mode (see also oprofile.timer
+				for generic hr timer mode)
 
 	oops=panic	Always panic on oopses. Default is to just kill the
 			process, but there is a small probability of

arch/x86/oprofile/nmi_int.c

@@ -613,24 +613,36 @@ static int __init p4_init(char **cpu_type)
 	return 0;
 }
 
-static int force_arch_perfmon;
-static int force_cpu_type(const char *str, struct kernel_param *kp)
+enum __force_cpu_type {
+	reserved = 0,		/* do not force */
+	timer,
+	arch_perfmon,
+};
+
+static int force_cpu_type;
+
+static int set_cpu_type(const char *str, struct kernel_param *kp)
 {
-	if (!strcmp(str, "arch_perfmon")) {
-		force_arch_perfmon = 1;
+	if (!strcmp(str, "timer")) {
+		force_cpu_type = timer;
+		printk(KERN_INFO "oprofile: forcing NMI timer mode\n");
+	} else if (!strcmp(str, "arch_perfmon")) {
+		force_cpu_type = arch_perfmon;
 		printk(KERN_INFO "oprofile: forcing architectural perfmon\n");
+	} else {
+		force_cpu_type = 0;
 	}
 
 	return 0;
 }
-module_param_call(cpu_type, force_cpu_type, NULL, NULL, 0);
+module_param_call(cpu_type, set_cpu_type, NULL, NULL, 0);
 
 static int __init ppro_init(char **cpu_type)
 {
 	__u8 cpu_model = boot_cpu_data.x86_model;
 	struct op_x86_model_spec *spec = &op_ppro_spec;	/* default */
 
-	if (force_arch_perfmon && cpu_has_arch_perfmon)
+	if (force_cpu_type == arch_perfmon && cpu_has_arch_perfmon)
 		return 0;
 
 	/*
@@ -697,6 +709,9 @@ int __init op_nmi_init(struct oprofile_operations *ops)
 	if (!cpu_has_apic)
 		return -ENODEV;
 
+	if (force_cpu_type == timer)
+		return -ENODEV;
+
 	switch (vendor) {
 	case X86_VENDOR_AMD:
 		/* Needs to be at least an Athlon (or hammer in 32bit mode) */