[RFC] perf tool & spe driver: shot at prctl errmsging

[Kim Phillips]

Example session: Lines beginning with "spe-pmu@" are new and
specify what the PMU driver found wrong to the user in a much
more precise manner:

$ ./perf record -e arm_spe_0// -C 0-3 true
Error:
spe-pmu@0: no sample period, or less than minimum (256)
PMU Hardware doesn't support sampling/overflow-interrupts.
$ ./perf record -e arm_spe_0// -C 0-3 -c 1024 true
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.022 MB perf.data ]
$ ./perf record -e arm_spe_0// -C 0-4 -c 1024 true
Error:
spe-pmu@0: not supported on CPU 4. Supported CPU list: 0-3
The arm_spe_0// event is not supported.
$ ./perf record -e arm_spe_0/pa_enable=1/ -C 0-3 -c 1024 true
Error:
spe-pmu@0: physical address and/or context ID capture limited to privileged users
$ sudo ./perf record -e arm_spe_0/pa_enable=1/ -C 0-3 -c 1024 true
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.071 MB perf.data ]
$

Signed-off-by: Kim Phillips <kim.phillips@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
- patch available and rebased on top of linux-will.git/perf/spe's latest, here:
	http://www.linux-arm.org/git?p=linux-kp.git;a=shortlog;h=refs/heads/spe-prctl
  or
	git://linux-arm.org/linux-kp.git  # spe-prctl branch

 drivers/perf/arm_spe_pmu.c | 46 ++++++++++++++++++++++++++++++++++++++--------
 tools/perf/perf.c          | 12 ++++++++++++
 tools/perf/util/evsel.c    | 14 +++++++++-----
 3 files changed, 59 insertions(+), 13 deletions(-)

diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
index fef0a4834879..cb4db7dac929 100644
--- a/drivers/perf/arm_spe_pmu.c
+++ b/drivers/perf/arm_spe_pmu.c
@@ -23,11 +23,13 @@
 #define DRVNAME				PMUNAME "_pmu"
 #define pr_fmt(fmt)			DRVNAME ": " fmt
 
+#include <linux/cpumask.h>
 #include <linux/cpuhotplug.h>
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/module.h>
 #include <linux/of_address.h>
+#include <linux/device.h>
 #include <linux/of_device.h>
 #include <linux/perf_event.h>
 #include <linux/platform_device.h>
@@ -660,20 +662,30 @@ static int arm_spe_pmu_event_init(struct perf_event *event)
 	u64 reg;
 	struct perf_event_attr *attr = &event->attr;
 	struct arm_spe_pmu *spe_pmu = to_spe_pmu(event->pmu);
+	const struct device *dev = &spe_pmu->pdev->dev;
+	const char *devname = dev_name(dev);
 
 	/* This is, of course, deeply driver-specific */
 	if (attr->type != event->pmu->type)
 		return -ENOENT;
 
 	if (event->cpu >= 0 &&
-	    !cpumask_test_cpu(event->cpu, &spe_pmu->supported_cpus))
+	    !cpumask_test_cpu(event->cpu, &spe_pmu->supported_cpus)) {
+		errorf("%s: not supported on CPU %d. Supported CPU list: %*pbl\n",
+		       devname, event->cpu, cpumask_pr_args(&spe_pmu->supported_cpus));
 		return -ENOENT;
+	}
 
-	if (arm_spe_event_to_pmsevfr(event) & PMSEVFR_EL1_RES0)
+	if (arm_spe_event_to_pmsevfr(event) & PMSEVFR_EL1_RES0) {
+		errorf("%s: unsupported Sampling Event Filter (PMSEVFR) value\n",
+		       devname);
 		return -EOPNOTSUPP;
+	}
 
-	if (attr->exclude_idle)
+	if (attr->exclude_idle) {
+		errorf("%s: Cannot exclude profiling when idle\n", devname);
 		return -EOPNOTSUPP;
+	}
 
 	/*
 	 * Feedback-directed frequency throttling doesn't work when we
@@ -682,26 +694,44 @@ static int arm_spe_pmu_event_init(struct perf_event *event)
 	 * count to reflect that. Instead, force the user to specify a
 	 * sample period instead.
 	 */
-	if (attr->freq)
+	if (attr->freq) {
+		errorf("%s: sample period must be specified\n", devname);
 		return -EINVAL;
+	}
+
+	if (!event->hw.sample_period ||
+	    event->hw.sample_period < spe_pmu->min_period) {
+		errorf("%s: no sample period, or less than minimum (%d)\n",
+		       devname, spe_pmu->min_period);
+		return -EOPNOTSUPP;
+	}
 
 	reg = arm_spe_event_to_pmsfcr(event);
 	if ((reg & BIT(PMSFCR_EL1_FE_SHIFT)) &&
-	    !(spe_pmu->features & SPE_PMU_FEAT_FILT_EVT))
+	    !(spe_pmu->features & SPE_PMU_FEAT_FILT_EVT)) {
+		errorf("%s: unsupported filter (EVT)\n", devname);
 		return -EOPNOTSUPP;
+	}
 
 	if ((reg & BIT(PMSFCR_EL1_FT_SHIFT)) &&
-	    !(spe_pmu->features & SPE_PMU_FEAT_FILT_TYP))
+	    !(spe_pmu->features & SPE_PMU_FEAT_FILT_TYP)) {
+		errorf("%s: unsupported filter (TYP)\n", devname);
 		return -EOPNOTSUPP;
+	}
 
 	if ((reg & BIT(PMSFCR_EL1_FL_SHIFT)) &&
-	    !(spe_pmu->features & SPE_PMU_FEAT_FILT_LAT))
+	    !(spe_pmu->features & SPE_PMU_FEAT_FILT_LAT)) {
+		errorf("%s: unsupported filter (LAT)\n", devname);
 		return -EOPNOTSUPP;
+	}
 
 	reg = arm_spe_event_to_pmscr(event);
 	if (!capable(CAP_SYS_ADMIN) &&
-	    (reg & (BIT(PMSCR_EL1_PA_SHIFT) | BIT(PMSCR_EL1_CX_SHIFT))))
+	    (reg & (BIT(PMSCR_EL1_PA_SHIFT) | BIT(PMSCR_EL1_CX_SHIFT)))) {
+		errorf("%s: physical address and/or context ID capture limited to privileged users\n",
+		       devname);
 		return -EACCES;
+	}
 
 	return 0;
 }
diff --git a/tools/perf/perf.c b/tools/perf/perf.c
index 628a5e412cb1..0d16dc5042ab 100644
--- a/tools/perf/perf.c
+++ b/tools/perf/perf.c
@@ -30,6 +30,13 @@
 #include <unistd.h>
 #include <linux/kernel.h>
 
+#include <fcntl.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+
+#define PR_ERRMSG_ENABLE		48
+#define PR_ERRMSG_READ			49
+
 const char perf_usage_string[] =
 	"perf [--version] [--help] [OPTIONS] COMMAND [ARGS]";
 
@@ -431,6 +438,11 @@ int main(int argc, const char **argv)
 	char sbuf[STRERR_BUFSIZE];
 	int value;
 
+	if (prctl(PR_ERRMSG_ENABLE, 1) < 0) {
+		perror("prctl/en");
+		exit(1);
+	}
+
 	/* libsubcmd init */
 	exec_cmd_init("perf", PREFIX, PERF_EXEC_PATH, EXEC_PATH_ENVIRONMENT);
 	pager_init(PERF_PAGER_ENVIRONMENT);
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index d9899280a9ee..e997a361d1eb 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -21,6 +21,7 @@
 #include <sys/ioctl.h>
 #include <sys/resource.h>
 #include <sys/types.h>
+#include <sys/prctl.h>
 #include <dirent.h>
 #include "asm/bug.h"
 #include "callchain.h"
@@ -40,6 +41,9 @@
 
 #include "sane_ctype.h"
 
+#define PR_ERRMSG_ENABLE		48
+#define PR_ERRMSG_READ			49
+
 static struct {
 	bool sample_id_all;
 	bool exclude_guest;
@@ -2518,19 +2522,19 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,
 			      int err, char *msg, size_t size)
 {
 	char sbuf[STRERR_BUFSIZE];
-	int printed = 0;
-	int n, perr;
+	int perr, printed = 0;
+	size_t n;
 
 	do {
 		errno = 0;
 		n = prctl(PR_ERRMSG_READ, sbuf, sizeof(sbuf));
 		perr = errno;
-		if (n > 0) {
-			printed = scnprintf(msg, n + 1, "%s\n", sbuf);
+		if (n > 0 && n < size) {
+			sbuf[n] = 0;
+			printed = scnprintf(msg, size, "%s", sbuf);
 			size -= printed;
 			msg += printed;
 		}
-		
 	} while (perr == 0);
 
 	switch (err) {
-- 
2.11.0