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Date:	Wed, 29 Apr 2015 20:04:51 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>
Cc:	dev@...yps.com, gusld@...ibm.com, <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 1/1] powerpc/hv-24x7: Check support before registering PMU

We currently try to register the 24x7 PMU unconditionally. Not all
Power systems support 24x7 counters (eg: Power7). On these systems
we get a backtrace during boot when trying to register the 24x7 PMU.

Check if the hypervisor supports 24x7 counters before attempting to
register the 24x7 PMU.

Reported-by: Gustavo Luiz Duarte <gusld@...ibm.com>
Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
---
 arch/powerpc/perf/hv-24x7.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/arch/powerpc/perf/hv-24x7.c b/arch/powerpc/perf/hv-24x7.c
index ec2eb20..19a59a3 100644
--- a/arch/powerpc/perf/hv-24x7.c
+++ b/arch/powerpc/perf/hv-24x7.c
@@ -1268,12 +1268,44 @@ static struct pmu h_24x7_pmu = {
 	.read        = h_24x7_event_read,
 };
 
+/*
+ * Return 1 if we can access the 24x7 counter catalog from the hypervisor.
+ * Return 0 otherwise.
+ */
+static int hv_has_24x7(void)
+{
+	int page_size = 4096;
+	unsigned long hret;
+	void *page;
+	struct hv_24x7_catalog_page_0 *page_0;
+
+	page_0 = kmalloc(page_size*2, GFP_KERNEL);
+	if (!page_0)
+		return 0;
+
+	/* buffer for catalog needs to be 4K-aligned */
+	page = (void *)((long)page_0 & (~page_size-1)) + page_size;
+	hret = h_get_24x7_catalog_page(page, 0, 0);
+	kfree(page_0);
+
+	if (hret) {
+		pr_devel("Error %ld reading catalog, disabling 24x7 PMU\n", hret);
+		return 0;
+	}
+
+	return 1;
+}
+
+
 static int hv_24x7_init(void)
 {
 	int r;
 	unsigned long hret;
 	struct hv_perf_caps caps;
 
+	if (!hv_has_24x7())
+		return -ENODEV;
+
 	if (!firmware_has_feature(FW_FEATURE_LPAR)) {
 		pr_debug("not a virtualized system, not enabling\n");
 		return -ENODEV;
-- 
1.8.3.1

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