Re: [PATCH 1/3] coresight: etm-perf: Add support for PID tracing for kernel at EL2

Leo Yan
2020-11-12T10:27:54Z

On Tue, Nov 10, 2020 at 06:33:11PM +0000, Suzuki Kuruppassery Poulose wrote:
> 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 VMID. 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 adds a new option, contextid_in_vmid as a separate config.
> Thus on an EL2 kernel, we will have two options available for
> the perf tool. However, to make it easier for the user to
> do pid tracing, we add a new format which will default to
> "contextid" (on EL1 kernel) or "contextid_in_vmid" (on EL2
> kernel). So that the user doesn't have to bother which EL the
> kernel is running.
>
> i.e, perf record -e cs_etm/pid/u --
>
> will always do the "pid" tracing, independent of the kernel EL.
>
> Also, the perf tool will be updated to automatically select
> "pid" config instead of the "contextid" for system wide/CPU wide
> mode.
>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Al Grant <al.grant@arm.com>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Leo Yan <leo.yan@linaro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
> drivers/hwtracing/coresight/coresight-etm-perf.c | 14 ++++++++++++++
> drivers/hwtracing/coresight/coresight-etm4x-core.c | 9 +++++++++
> include/linux/coresight-pmu.h | 11 +++++++----
> 3 files changed, 30 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index bdc34ca449f7..f763def145e4 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -30,14 +30,28 @@ static DEFINE_PER_CPU(struct coresight_device *, csdev_src);
> /* ETMv3.5/PTM's ETMCR is 'config' */
> PMU_FORMAT_ATTR(cycacc, "config:" __stringify(ETM_OPT_CYCACC));
> PMU_FORMAT_ATTR(contextid, "config:" __stringify(ETM_OPT_CTXTID));
> +PMU_FORMAT_ATTR(contextid_in_vmid, "config:" __stringify(ETM_OPT_CTXTID_IN_VMID));
> 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");
>
> +static ssize_t format_attr_pid_show(struct device *dev,
> + struct device_attribute *attr,
> + char *page)
> +{
> + int pid_fmt = is_kernel_in_hyp_mode() ? ETM_OPT_CTXTID_IN_VMID : ETM_OPT_CTXTID;
> +
> + return sprintf(page, "config:%d\n", pid_fmt);
> +}
> +
> +struct device_attribute format_attr_pid = __ATTR(pid, 0444, format_attr_pid_show, NULL);
> +
> static struct attribute *etm_config_formats_attr[] = {
> &format_attr_cycacc.attr,
> &format_attr_contextid.attr,
> + &format_attr_contextid_in_vmid.attr,
> + &format_attr_pid.attr,
> &format_attr_timestamp.attr,
> &format_attr_retstack.attr,
> &format_attr_sinkid.attr,
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index d78a37b6592c..8cb2cb1febce 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -382,6 +382,15 @@ static int etm4_parse_event_config(struct etmv4_drvdata *drvdata,
> /* bit[6], Context ID tracing bit */
> config->cfg |= BIT(ETM4_CFG_BIT_CTXTID);
>
> + /* Do not enable VMID tracing if we are not running in EL2 */
> + if (attr->config & BIT(ETM_OPT_CTXTID_IN_VMID)) {
> + if (!is_kernel_in_hyp_mode()) {
> + ret = -EINVAL;
> + goto out;
> + }
> + config->cfg |= BIT(ETM4_CFG_BIT_VMID) | BIT(ETM4_CFG_BIT_VMID_OPT);
> + }
> +

Nitpick: should the driver need to check the kernel running mode for the
config ETM_OPT_CTXTID? I.e. if the BIT(ETM_OPT_CTXTID) is set in
"attr->config", does it mean the kernel should run in EL1 mode?

Just curious, does there have a scenario that we need to set BIT
ETM4_CFG_BIT_VMID but the bit ETM4_CFG_BIT_VMID_OPT is cleared? I
think a bit for this, but cannot find a situation for tracing context
ID based on VTTBR_EL2.VMID. So this might be not a question for us.

Thanks,
Leo

> /* 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 b0e35eec6499..927c6285ce5d 100644
> --- a/include/linux/coresight-pmu.h
> +++ b/include/linux/coresight-pmu.h
> @@ -11,16 +11,19 @@
> #define CORESIGHT_ETM_PMU_SEED 0x10
>
> /* ETMv3.5/PTM's ETMCR config bit */
> -#define ETM_OPT_CYCACC 12
> -#define ETM_OPT_CTXTID 14
> -#define ETM_OPT_TS 28
> -#define ETM_OPT_RETSTK 29
> +#define ETM_OPT_CYCACC 12
> +#define ETM_OPT_CTXTID 14
> +#define ETM_OPT_CTXTID_IN_VMID 15
> +#define ETM_OPT_TS 28
> +#define ETM_OPT_RETSTK 29
>
> /* ETMv4 CONFIGR programming bits for the ETM OPTs */
> #define ETM4_CFG_BIT_CYCACC 4
> #define ETM4_CFG_BIT_CTXTID 6
> +#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)
> {
> --
> 2.24.1