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Subject[PATCH v3 3/8] coresight: etm-perf: Support PID tracing for kernel at EL2
From: Suzuki K Poulose <>

When the kernel is running at EL2, the PID is stored in CONTEXTIDR_EL2.
So, tracing CONTEXTIDR_EL1 doesn't give us the pid of the process.
Thus we should trace the VMID with VMIDOPT set to trace CONTEXTIDR_EL2
instead of CONTEXTIDR_EL1. Given that we have an existing config
option "contextid" and this will be useful for tracing virtual machines
(when we get to support virtualization).

So instead, this patch extends option CTXTID with an extra bit
ETM_OPT_CTXTID2 (bit 15), thus on an EL2 kernel, we will have another
bit available for the perf tool: ETM_OPT_CTXTID is for kernel running in
EL1, ETM_OPT_CTXTID2 is used when kernel runs in EL2 with VHE enabled.

The tool must be backward compatible for users, i.e, "contextid" today
traces PID and that should remain the same; for this purpose, the perf
tool is updated to automatically set corresponding bit for the
"contextid" config, therefore, the user doesn't have to bother which EL
the kernel is running.

i.e, perf record -e cs_etm/contextid/u --

will always do the "pid" tracing, independent of the kernel EL.

The driver parses the format "contextid", which traces CONTEXTIDR_EL1
for ETM_OPT_CTXTID (on EL1 kernel) and traces CONTEXTIDR_EL2 for
ETM_OPT_CTXTID2 (on EL2 kernel).

Besides the enhancement for format "contexid", extra two formats are
introduced: "contextid1" and "contextid2". This considers to support
tracing both CONTEXTIDR_EL1 and CONTEXTIDR_EL2 when the kernel is
running at EL2. Finally, the PMU formats are defined as follow:

"contextid1": Available on both EL1 kernel and EL2 kernel. When the
kernel is running at EL1, "contextid1" enables the PID
tracing; when the kernel is running at EL2, this enables
tracing the PID of guest applications.

"contextid2": Only usable when the kernel is running at EL2. When
selected, enables PID tracing on EL2 kernel.

"contextid": Will be an alias for the option that enables PID
tracing. I.e,
contextid == contextid1, on EL1 kernel.
contextid == contextid2, on EL2 kernel.

Cc: Mathieu Poirier <>
Cc: Al Grant <>
Cc: Mike Leach <>
Cc: Leo Yan <>
Signed-off-by: Suzuki K Poulose <>
[ Added two config formats: contextid1, contextid2 ]
Signed-off-by: Leo Yan <>
Reviewed-by: Mike Leach <>
.../hwtracing/coresight/coresight-etm-perf.c | 27 ++++++++++++++++++-
.../coresight/coresight-etm4x-core.c | 13 +++++++++
include/linux/coresight-pmu.h | 3 +++
3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index 465ef1aa8c82..0f603b4094f2 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -32,15 +32,40 @@ static DEFINE_PER_CPU(struct coresight_device *, csdev_src);
* now take them as general formats and apply on all ETMs.
PMU_FORMAT_ATTR(cycacc, "config:" __stringify(ETM_OPT_CYCACC));
-PMU_FORMAT_ATTR(contextid, "config:" __stringify(ETM_OPT_CTXTID));
+/* contextid1 enables tracing CONTEXTIDR_EL1 for ETMv4 */
+PMU_FORMAT_ATTR(contextid1, "config:" __stringify(ETM_OPT_CTXTID));
+/* contextid2 enables tracing CONTEXTIDR_EL2 for ETMv4 */
+PMU_FORMAT_ATTR(contextid2, "config:" __stringify(ETM_OPT_CTXTID2));
PMU_FORMAT_ATTR(timestamp, "config:" __stringify(ETM_OPT_TS));
PMU_FORMAT_ATTR(retstack, "config:" __stringify(ETM_OPT_RETSTK));
/* Sink ID - same for all ETMs */
PMU_FORMAT_ATTR(sinkid, "config2:0-31");

+ * contextid always traces the "PID". The PID is in CONTEXTIDR_EL1
+ * when the kernel is running at EL1; when the kernel is at EL2,
+ * the PID is in CONTEXTIDR_EL2.
+ */
+static ssize_t format_attr_contextid_show(struct device *dev,
+ struct device_attribute *attr,
+ char *page)
+ int pid_fmt = ETM_OPT_CTXTID;
+ pid_fmt = is_kernel_in_hyp_mode() ? ETM_OPT_CTXTID2 : ETM_OPT_CTXTID;
+ return sprintf(page, "config:%d\n", pid_fmt);
+struct device_attribute format_attr_contextid =
+ __ATTR(contextid, 0444, format_attr_contextid_show, NULL);
static struct attribute *etm_config_formats_attr[] = {
+ &format_attr_contextid1.attr,
+ &format_attr_contextid2.attr,
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index b20b6ff17cf6..8681c225b0ba 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -477,6 +477,19 @@ static int etm4_parse_event_config(struct etmv4_drvdata *drvdata,
/* bit[6], Context ID tracing bit */
config->cfg |= BIT(ETM4_CFG_BIT_CTXTID);

+ /*
+ * If set bit ETM_OPT_CTXTID2 in perf config, this asks to trace VMID
+ * for recording CONTEXTIDR_EL2. Do not enable VMID tracing if the
+ * kernel is not running in EL2.
+ */
+ if (attr->config & BIT(ETM_OPT_CTXTID2)) {
+ if (!is_kernel_in_hyp_mode()) {
+ ret = -EINVAL;
+ goto out;
+ }
+ }
/* return stack - enable if selected and supported */
if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
/* bit[12], Return stack enable bit */
diff --git a/include/linux/coresight-pmu.h b/include/linux/coresight-pmu.h
index 5dc47cfdcf07..4ac5c081af93 100644
--- a/include/linux/coresight-pmu.h
+++ b/include/linux/coresight-pmu.h
@@ -20,14 +20,17 @@
#define ETM_OPT_CYCACC 12
#define ETM_OPT_CTXTID 14
+#define ETM_OPT_CTXTID2 15
#define ETM_OPT_TS 28
#define ETM_OPT_RETSTK 29

/* ETMv4 CONFIGR programming bits for the ETM OPTs */
+#define ETM4_CFG_BIT_VMID 7
#define ETM4_CFG_BIT_TS 11
#define ETM4_CFG_BIT_RETSTK 12
+#define ETM4_CFG_BIT_VMID_OPT 15

static inline int coresight_get_trace_id(int cpu)
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