Re: [PATCH v3 3/5] coresight: etm4x: fix inconsistencies with sysfs configration

Jie Gan
2026-04-13T02:38:17Z

Hi Yeoreum,

On 4/13/2026 1:55 AM, Yeoreum Yun wrote:
> The current ETM4x configuration via sysfs can lead to the following
> inconsistencies:
>
> - If a configuration is modified via sysfs while a perf session is
> active, the running configuration may differ between before
> a sched-out and after a subsequent sched-in.
>
> - If a perf session and sysfs session tries to enable concurrently,
> configuration from configfs could be corrupted.
>
> - There is chance to corrupt drvdata->config if perf session tries
> to enabled among handling cscfg_csdev_disable_active_config()
> in etm4_disable_sysfs().
>
> To resolve these inconsistencies, the configuration should be separated into:
>
> - active_config, which is applied configuration for the current session
> - config, which stores the settings configured via sysfs.
>
> and apply configuration from configfs after taking a mode.

typo in subject:
s/configration/configuration

>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
> .../hwtracing/coresight/coresight-etm4x-cfg.c | 2 +-
> .../coresight/coresight-etm4x-core.c | 74 ++++++++++++-------
> drivers/hwtracing/coresight/coresight-etm4x.h | 2 +
> 3 files changed, 49 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> index d14d7c8a23e5..0553771d04e7 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> @@ -47,7 +47,7 @@ static int etm4_cfg_map_reg_offset(struct etmv4_drvdata *drvdata,
> struct cscfg_regval_csdev *reg_csdev, u32 offset)
> {
> int err = -EINVAL, idx;
> - struct etmv4_config *drvcfg = &drvdata->config;
> + struct etmv4_config *drvcfg = &drvdata->active_config;
> u32 off_mask;

<...>

> struct device *etm_dev = &csdev->dev;
> struct csdev_access *csa = &csdev->access;
> @@ -616,19 +621,36 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
> static void etm4_enable_sysfs_smp_call(void *info)
> {
> struct etm4_enable_arg *arg = info;
> + struct etmv4_drvdata *drvdata;
> struct coresight_device *csdev;
>
> if (WARN_ON(!arg))
> return;
>
> - csdev = arg->drvdata->csdev;
> + drvdata = arg->drvdata;
> + csdev = drvdata->csdev;
> if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
> /* Someone is already using the tracer */
> arg->rc = -EBUSY;
> return;
> }
>
> - arg->rc = etm4_enable_hw(arg->drvdata);
> + drvdata->active_config = drvdata->config;
> +
> + if (arg->cfg_hash) {
> + arg->rc = cscfg_csdev_enable_active_config(csdev,
> + arg->cfg_hash,
> + arg->preset);
> + if (arg->rc)

we need reset the mode once enable failed before return.
coresight_set_mode(csdev, CS_MODE_DISABLED);

Thanks,
Jie

> + return;
> + }
> +
> + drvdata->trcid = arg->trace_id;
> +
> + /* Tracer will never be paused in sysfs mode */
> + drvdata->paused = false;
> +
> + arg->rc = etm4_enable_hw(drvdata);
>
> /* The tracer didn't start */
> if (arg->rc)
> @@ -670,7 +692,7 @@ static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata,
> int ctridx;
> int rselector;
> const struct etmv4_caps *caps = &drvdata->caps;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
>
> /* No point in trying if we don't have at least one counter */
> if (!caps->nr_cntr)
> @@ -754,7 +776,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
> int ret = 0;
> struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> const struct etmv4_caps *caps = &drvdata->caps;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
> struct perf_event_attr max_timestamp = {
> .ATTR_CFG_FLD_timestamp_CFG = U64_MAX,
> };
> @@ -916,24 +938,18 @@ static int etm4_enable_sysfs(struct coresight_device *csdev, struct coresight_pa
>
> /* enable any config activated by configfs */
> cscfg_config_sysfs_get_active_cfg(&cfg_hash, &preset);
> - if (cfg_hash) {
> - ret = cscfg_csdev_enable_active_config(csdev, cfg_hash, preset);
> - if (ret)
> - return ret;
> - }
>
> raw_spin_lock(&drvdata->spinlock);
>
> - drvdata->trcid = path->trace_id;
> -
> - /* Tracer will never be paused in sysfs mode */
> - drvdata->paused = false;
> -
> /*
> * Executing etm4_enable_hw on the cpu whose ETM is being enabled
> * ensures that register writes occur when cpu is powered.
> */
> arg.drvdata = drvdata;
> + arg.cfg_hash = cfg_hash;
> + arg.preset = preset;
> + arg.trace_id = path->trace_id;
> +
> ret = smp_call_function_single(drvdata->cpu,
> etm4_enable_sysfs_smp_call, &arg, 1);
> if (!ret)
> @@ -1034,7 +1050,7 @@ static void etm4_disable_hw(struct etmv4_drvdata *drvdata)
> {
> u32 control;
> const struct etmv4_caps *caps = &drvdata->caps;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
> struct coresight_device *csdev = drvdata->csdev;
> struct csdev_access *csa = &csdev->access;
> int i;
> @@ -1070,6 +1086,8 @@ static void etm4_disable_sysfs_smp_call(void *info)
>
> etm4_disable_hw(drvdata);
>
> + cscfg_csdev_disable_active_config(drvdata->csdev);
> +
> coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
> }
>
> @@ -1130,9 +1148,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
> drvdata, 1);
>
> raw_spin_unlock(&drvdata->spinlock);
> -
> - cscfg_csdev_disable_active_config(csdev);
> -
> cpus_read_unlock();
>
> /*
> @@ -1375,6 +1390,7 @@ static void etm4_init_arch_data(void *info)
> struct etm4_init_arg *init_arg = info;
> struct etmv4_drvdata *drvdata;
> struct etmv4_caps *caps;
> + struct etmv4_config *config;
> struct csdev_access *csa;
> struct device *dev = init_arg->dev;
> int i;
> @@ -1382,6 +1398,7 @@ static void etm4_init_arch_data(void *info)
> drvdata = dev_get_drvdata(init_arg->dev);
> caps = &drvdata->caps;
> csa = init_arg->csa;
> + config = &drvdata->active_config;
>
> /*
> * If we are unable to detect the access mechanism,
> @@ -1442,7 +1459,7 @@ static void etm4_init_arch_data(void *info)
>
> /* EXLEVEL_S, bits[19:16] Secure state instruction tracing */
> caps->s_ex_level = FIELD_GET(TRCIDR3_EXLEVEL_S_MASK, etmidr3);
> - drvdata->config.s_ex_level = caps->s_ex_level;
> + config->s_ex_level = caps->s_ex_level;
> /* EXLEVEL_NS, bits[23:20] Non-secure state instruction tracing */
> caps->ns_ex_level = FIELD_GET(TRCIDR3_EXLEVEL_NS_MASK, etmidr3);
> /*
> @@ -1687,7 +1704,7 @@ static void etm4_set_default(struct etmv4_config *config)
> static int etm4_get_next_comparator(struct etmv4_drvdata *drvdata, u32 type)
> {
> int nr_comparator, index = 0;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
>
> /*
> * nr_addr_cmp holds the number of comparator _pair_, so time 2
> @@ -1728,7 +1745,7 @@ static int etm4_set_event_filters(struct etmv4_drvdata *drvdata,
> {
> int i, comparator, ret = 0;
> u64 address;
> - struct etmv4_config *config = &drvdata->config;
> + struct etmv4_config *config = &drvdata->active_config;
> struct etm_filters *filters = event->hw.addr_filters;
>
> if (!filters)
> @@ -2250,7 +2267,8 @@ static int etm4_add_coresight_dev(struct etm4_init_arg *init_arg)
> if (!desc.name)
> return -ENOMEM;
>
> - etm4_set_default(&drvdata->config);
> + etm4_set_default(&drvdata->active_config);
> + drvdata->config = drvdata->active_config;
>
> pdata = coresight_get_platform_data(dev);
> if (IS_ERR(pdata))
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index 3cc1ca76c933..b943c28c9c71 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -1069,6 +1069,7 @@ struct etmv4_save_state {
> * allows tracing at all ELs. We don't want to compute this
> * at runtime, due to the additional setting of TRFCR_CX when
> * in EL2. Otherwise, 0.
> + * @active_config: structure holding current applied configuration parameters.
> * @config: structure holding configuration parameters.
> * @save_state: State to be preserved across power loss
> * @paused: Indicates if the trace unit is paused.
> @@ -1089,6 +1090,7 @@ struct etmv4_drvdata {
> bool os_unlock : 1;
> bool paused : 1;
> u64 trfcr;
> + struct etmv4_config active_config;
> struct etmv4_config config;
> struct etmv4_save_state *save_state;
> DECLARE_BITMAP(arch_features, ETM4_IMPDEF_FEATURE_MAX);