powerpc/perf: Infrastructure to support checking of attr.config*

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 some specific values for
bit fields are reserved. For ex., MMCRA[61:62] is
Random Sampling Mode (SM) and value of 0b11 for this field
is reserved.

Writing non-zero or invalid values in these 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.
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210408074504.248211-1-maddy@linux.ibm.com

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);
 };
 
 /*

arch/powerpc/perf/core-book3s.c

@@ -1963,6 +1963,17 @@ static int power_pmu_event_init(struct perf_event *event)
 		return -ENOENT;
 	}
 
+	/*
+	 * PMU config registers have fields that are
+	 * reserved and some specific values for bit fields are reserved.
+	 * For ex., MMCRA[61:62] is Randome Sampling Mode (SM)
+	 * and value of 0b11 to this field is reserved.
+	 * Check for invalid values in attr.config.
+	 */
+	if (ppmu->check_attr_config &&
+	    ppmu->check_attr_config(event))
+		return -EINVAL;
+
 	event->hw.config_base = ev;
 	event->hw.idx = 0;