Subject: [PATCH V2 1/2] powerpc/perf: Infrastructure to support checking of attr.config*

From: Madhavan Srinivasan <[email-masked]>
Date: Fri, 26 Feb 2021 12:20:24 +0530

Introduce code to support the checking of attr.config* for
values which are reserved for a given platform.
Performance Monitoring Unit (PMU) configuration registers
have fields that are reserved and specific value to bit field
as reserved. For ex., MMCRA[61:62] is Randome Sampling Mode (SM)
and value of 0b11 to this field is reserved.

Writing a non-zero values in these fields or writing invalid
value to bit fields will have unknown behaviours.

Patch adds a generic call-back function "check_attr_config"
in "struct power_pmu", to be called in event_init to
check for attr.config* values for a given platform.
"check_attr_config" is valid only for raw event type.

Signed-off-by: Madhavan Srinivasan <[email-masked]>
---
Changelog v1:
-Fixed commit message and in-code comments

 arch/powerpc/include/asm/perf_event_server.h |  6 ++++++
 arch/powerpc/perf/core-book3s.c              | 14 ++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/powerpc/include/asm/perf_event_server.h b/arch/powerpc/include/asm/perf_event_server.h
index 00e7e671bb4b..dde97d7d9253 100644
--- a/arch/powerpc/include/asm/perf_event_server.h
+++ b/arch/powerpc/include/asm/perf_event_server.h
@@ -67,6 +67,12 @@ struct power_pmu {
 	 * the pmu supports extended perf regs capability
 	 */
 	int		capabilities;
+	/*
+	 * Function to check event code for values which are
+	 * reserved. Function takes struct perf_event as input,
+	 * since event code could be spread in attr.config*
+	 */
+	int		(*check_attr_config)(struct perf_event *ev);
 };
 
 /*
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 6817331e22ff..c6eeb4fdc5fd 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -1958,6 +1958,20 @@ static int power_pmu_event_init(struct perf_event *event)
 
 		if (ppmu->blacklist_ev && is_event_blacklisted(ev))
 			return -EINVAL;
+		/*
+		 * PMU config registers have fields that are
+		 * reserved and specific value to bit field as reserved.
+		 * For ex., MMCRA[61:62] is Randome Sampling Mode (SM)
+		 * and value of 0b11 to this field is reserved.
+		 *
+		 * This check is needed only for raw event type,
+		 * since tools like fuzzer use raw event type to
+		 * provide randomized event code values for test.
+		 *
+		 */
+		if (ppmu->check_attr_config &&
+		    ppmu->check_attr_config(event))
+			return -EINVAL;
 		break;
 	default:
 		return -ENOENT;
-- 
2.26.2