perf/x86/intel/pt: Fix KVM warning due to doing rdmsr() before the CPUID test

If KVM does not support INTEL_PT, guest MSR_IA32_RTIT_CTL reading will
produce host warning like "kvm [2469]: vcpu0 unhandled rdmsr: 0x570".

Guest can determine whether the CPU supports Intel_PT according to CPUID,
so test_cpu_cap function is added before rdmsr,and it is more in line with
the code style.

Signed-off-by: Huaitong Han <huaitong.han@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: acme@kernel.org
Link: http://lkml.kernel.org/r/1441009262-9792-1-git-send-email-huaitong.han@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/perf_event_intel_pt.c

@@ -139,9 +139,6 @@ static int __init pt_pmu_hw_init(void)
 	long i;
 
 	attrs = NULL;
-	ret = -ENODEV;
-	if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_INTEL_PT))
-		goto fail;
 
 	for (i = 0; i < PT_CPUID_LEAVES; i++) {
 		cpuid_count(20, i,
@@ -1130,6 +1127,10 @@ static __init int pt_init(void)
 	int ret, cpu, prior_warn = 0;
 
 	BUILD_BUG_ON(sizeof(struct topa) > PAGE_SIZE);
+
+	if (!test_cpu_cap(&boot_cpu_data, X86_FEATURE_INTEL_PT))
+		return -ENODEV;
+
 	get_online_cpus();
 	for_each_online_cpu(cpu) {
 		u64 ctl;