perf_counter: fix fixed-purpose counter support on v2 Intel-PERFMON

Fixed-purpose counters stopped working in a simple 'perf stat ls' run:

   <not counted>  cache references
   <not counted>  cache misses

Due to:

  ef7b3e09: perf_counter, x86: remove vendor check in fixed_mode_idx()

Which made x86_pmu.num_counters_fixed matter: if it's nonzero, the
fixed-purpose counters are utilized.

But on v2 perfmon this field is not set (despite there being
fixed-purpose PMCs). So add a quirk to set the number of fixed-purpose
counters to at least three.

[ Impact: add quirk for three fixed-purpose counters on certain Intel CPUs ]

Cc: Robert Richter <robert.richter@amd.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1241002046-8832-28-git-send-email-robert.richter@amd.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/perf_counter.c

@@ -962,7 +962,13 @@ static int intel_pmu_init(void)
 	x86_pmu = intel_pmu;
 	x86_pmu.version = version;
 	x86_pmu.num_counters = eax.split.num_counters;
-	x86_pmu.num_counters_fixed = edx.split.num_counters_fixed;
+
+	/*
+	 * Quirk: v2 perfmon does not report fixed-purpose counters, so
+	 * assume at least 3 counters:
+	 */
+	x86_pmu.num_counters_fixed = max((int)edx.split.num_counters_fixed, 3);
+
 	x86_pmu.counter_bits = eax.split.bit_width;
 	x86_pmu.counter_mask = (1ULL << eax.split.bit_width) - 1;