cpufreq / intel_pstate: Add function to check that all MSRs are valid

Some VMs seem to try to implement some MSRs but not all the registers
the driver needs. Check to make sure all the MSR that we need are
available. If any of the required MSRs are not available refuse to
load.

References: https://bugzilla.redhat.com/show_bug.cgi?id=922923
Reported-by: Josh Stone <[e-mail]>
Signed-off-by: Dirk Brandewie <[e-mail]>
Acked-by: Viresh Kumar <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/cpufreq/intel_pstate.c

···
 
 static int __initdata no_load;
 
+static int intel_pstate_msrs_not_valid(void)
+{
+	/* Check that all the msr's we are using are valid. */
+	u64 aperf, mperf, tmp;
+
+	rdmsrl(MSR_IA32_APERF, aperf);
+	rdmsrl(MSR_IA32_MPERF, mperf);
+
+	if (!intel_pstate_min_pstate() ||
+		!intel_pstate_max_pstate() ||
+		!intel_pstate_turbo_pstate())
+		return -ENODEV;
+
+	rdmsrl(MSR_IA32_APERF, tmp);
+	if (!(tmp - aperf))
+		return -ENODEV;
+
+	rdmsrl(MSR_IA32_MPERF, tmp);
+	if (!(tmp - mperf))
+		return -ENODEV;
+
+	return 0;
+}
 static int __init intel_pstate_init(void)
 {
 	int cpu, rc = 0;
···
 
 	id = x86_match_cpu(intel_pstate_cpu_ids);
 	if (!id)
+		return -ENODEV;
+
+	if (intel_pstate_msrs_not_valid())
 		return -ENODEV;
 
 	pr_info("Intel P-state driver initializing.\n");