[PATCH v2] perf/x86: check ucode before disabling PEBS on SandyBridge

[Stephane Eranian <eranian@google.com>]

PEBS on SandyBridge model 42 (desktop, mobile), and 45 (SNB-EP).
was disabled for both models due to an erratum.
    
A workaround is implemented by micro-code from version 0x28.

This patch checks the microcode version and prevent creation
of a PEBS event if version < 0x28. The check is done each time
a PEBS event is created and NOT at boot time because the
micro-code update may only be done after the kernel has booted.

Go to downloadcenter.intel.com to download microcode updates.
Search for microcode, download update dated 6/6/2012 or later.

Signed-off-by: Stephane Eranian <eranian@google.com>
---

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 5ec146c..d4d2597 100644
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -1394,6 +1394,25 @@ static void intel_pebs_aliases_snb(struct perf_event *event)
 	}
 }
 
+static int check_pebs_quirks(void)
+{
+	int uversion = cpu_data(smp_processor_id()).microcode;
+	int model = cpu_data(smp_processor_id()).x86_model;
+
+	/* do not have PEBS to begin with */
+	if (!x86_pmu.pebs)
+		return 0;
+	/*
+	 * check ucode version for SNB, SNB-EP
+	 * they need ucode 0x28 or later for PEBS
+	 * to be operational
+	 */
+	if ((model == 42 || model == 45) && uversion < 0x28)
+		return -ENOTSUPP;
+
+	return 0;
+}
+
 static int intel_pmu_hw_config(struct perf_event *event)
 {
 	int ret = x86_pmu_hw_config(event);
@@ -1401,8 +1420,14 @@ static int intel_pmu_hw_config(struct perf_event *event)
 	if (ret)
 		return ret;
 
-	if (event->attr.precise_ip && x86_pmu.pebs_aliases)
-		x86_pmu.pebs_aliases(event);
+	if (event->attr.precise_ip) {
+
+		if (check_pebs_quirks())
+			return -ENOTSUPP;
+
+		if (x86_pmu.pebs_aliases)
+			x86_pmu.pebs_aliases(event);
+	}
 
 	if (intel_pmu_needs_lbr_smpl(event)) {
 		ret = intel_pmu_setup_lbr_filter(event);
@@ -1716,9 +1741,17 @@ static __init void intel_clovertown_quirk(void)
 
 static __init void intel_sandybridge_quirk(void)
 {
-	pr_warn("PEBS disabled due to CPU errata\n");
-	x86_pmu.pebs = 0;
-	x86_pmu.pebs_constraints = NULL;
+	int uversion = cpu_data(smp_processor_id()).microcode;
+	int model = cpu_data(smp_processor_id()).x86_model;
+	/*
+	 * check ucode version for SNB, SNB-EP
+	 */
+	if ((model == 42 || model == 45) && uversion < 0x28) {
+		pr_warn("perf_events: SandyBridge PEBS unavailable due to"
+			" CPU erratum, update microcode (was 0x%x, needs "
+			"at least version 0x28).\n",
+			uversion);
+	}
 }
 
 static const struct { int id; char *name; } intel_arch_events_map[] __initconst = {