s390/cpum_sf: prohibit callchain data collection

CPU Measurement sampling facility on s390 does not support
perf tool collection of callchain data using --call-graph
option. The sampling facility collects samples in a ring
buffer which includes only the instruction address the
samples were taken. When the ring buffer hits a watermark,
a measurement alert interrupt is triggered and handled
by the performance measurement unit (PMU) device driver.
It collects the samples and feeds each sample to the
perf ring buffer in the common code via functions
perf_prepare_sample()/perf_output_sample(). When function
perf_prepare_sample() is called to collect sample data's
callchain, user register values or stack area, invalid
data is picked, because the context of the collected
information does not match the context when the sample
was taken.

There is currently no way to provide the callchain and other
information, because the hardware sampler does not collect this
information.

Therefore prohibit sampling when the user requests a callchain graph
from the hardware sampler. Return -EOPNOTSUPP to the user in this
case.
If call chains are really wanted, users need to specify software
event cpu-clock to get the callchain information from a
software event.

Signed-off-by: Thomas Richter <[email protected]>
Reviewed-by: Sumanth Korikkar <[email protected]>
Signed-off-by: Heiko Carstens <[email protected]>

Author: Thomas Richter

arch/s390/kernel/perf_cpum_sf.c

@@ -881,12 +881,21 @@ static int __hw_perf_event_init(struct perf_event *event)
 	return err;
 }
 
+static bool is_callchain_event(struct perf_event *event)
+{
+	u64 sample_type = event->attr.sample_type;
+
+	return sample_type & (PERF_SAMPLE_CALLCHAIN | PERF_SAMPLE_REGS_USER |
+			      PERF_SAMPLE_STACK_USER);
+}
+
 static int cpumsf_pmu_event_init(struct perf_event *event)
 {
 	int err;
 
 	/* No support for taken branch sampling */
-	if (has_branch_stack(event))
+	/* No support for callchain, stacks and registers */
+	if (has_branch_stack(event) || is_callchain_event(event))
 		return -EOPNOTSUPP;
 
 	switch (event->attr.type) {