Re: [PATCH v4 4/9] coresight: etm4x: fix inconsistencies with sysfs configuration

[Jie Gan <jie.gan@oss.qualcomm.com>]

On 4/13/2026 10:19 PM, Yeoreum Yun wrote:
> The current ETM4x configuration via sysfs can lead to
> several inconsistencies:
> 
>    - If the configuration is modified via sysfs while a perf session is
>      active, the running configuration may differ before a sched-out and
>      after a subsequent sched-in.
> 
>    - If a perf session and a sysfs session enable tracing concurrently,
>      the configuration from configfs may become corrupted.
> 
>    - There is a risk of corrupting drvdata->config if a perf session enables
>      tracing while cscfg_csdev_disable_active_config() is being handled in
>      etm4_disable_sysfs().
> 
> To resolve these issues, separate the configuration into:
> 
>    - active_config: the configuration applied to the current session
>    - config: the configuration set via sysfs
> 
> Additionally:
> 
>    - Apply the configuration from configfs after taking the appropriate mode.
> 
>    - Since active_config and related fields are accessed only by the local CPU
>      in etm4_enable/disable_sysfs_smp_call() (similar to perf enable/disable),
>      remove the lock/unlock from the sysfs enable/disable path and
>      startup/dying_cpu except when to access config fields.
> 
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>   .../hwtracing/coresight/coresight-etm4x-cfg.c |   2 +-
>   .../coresight/coresight-etm4x-core.c          | 107 ++++++++++--------
>   drivers/hwtracing/coresight/coresight-etm4x.h |   2 +
>   3 files changed, 62 insertions(+), 49 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;
>   
>   	if (((offset >= TRCEVENTCTL0R) && (offset <= TRCVIPCSSCTLR)) ||
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 1bc9f13e33f7..01099689525b 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -245,6 +245,10 @@ void etm4_release_trace_id(struct etmv4_drvdata *drvdata)
>   
>   struct etm4_enable_arg {
>   	struct etmv4_drvdata *drvdata;
> +	unsigned long cfg_hash;
> +	int preset;
> +	u8 trace_id;
> +	struct etmv4_config config;
>   	int rc;
>   };
>   
> @@ -270,10 +274,11 @@ static void etm4x_prohibit_trace(struct etmv4_drvdata *drvdata)
>   static u64 etm4x_get_kern_user_filter(struct etmv4_drvdata *drvdata)
>   {
>   	u64 trfcr = drvdata->trfcr;
> +	struct etmv4_config *config = &drvdata->active_config;
>   
> -	if (drvdata->config.mode & ETM_MODE_EXCL_KERN)
> +	if (config->mode & ETM_MODE_EXCL_KERN)
>   		trfcr &= ~TRFCR_EL1_ExTRE;
> -	if (drvdata->config.mode & ETM_MODE_EXCL_USER)
> +	if (config->mode & ETM_MODE_EXCL_USER)
>   		trfcr &= ~TRFCR_EL1_E0TRE;
>   
>   	return trfcr;
> @@ -281,7 +286,7 @@ static u64 etm4x_get_kern_user_filter(struct etmv4_drvdata *drvdata)
>   
>   /*
>    * etm4x_allow_trace - Allow CPU tracing in the respective ELs,
> - * as configured by the drvdata->config.mode for the current
> + * as configured by the drvdata->active_config.mode for the current
>    * session. Even though we have TRCVICTLR bits to filter the
>    * trace in the ELs, it doesn't prevent the ETM from generating
>    * a packet (e.g, TraceInfo) that might contain the addresses from
> @@ -292,12 +297,13 @@ static u64 etm4x_get_kern_user_filter(struct etmv4_drvdata *drvdata)
>   static void etm4x_allow_trace(struct etmv4_drvdata *drvdata)
>   {
>   	u64 trfcr, guest_trfcr;
> +	struct etmv4_config *config = &drvdata->active_config;
>   
>   	/* If the CPU doesn't support FEAT_TRF, nothing to do */
>   	if (!drvdata->trfcr)
>   		return;
>   
> -	if (drvdata->config.mode & ETM_MODE_EXCL_HOST)
> +	if (config->mode & ETM_MODE_EXCL_HOST)
>   		trfcr = drvdata->trfcr & ~(TRFCR_EL1_ExTRE | TRFCR_EL1_E0TRE);
>   	else
>   		trfcr = etm4x_get_kern_user_filter(drvdata);
> @@ -305,7 +311,7 @@ static void etm4x_allow_trace(struct etmv4_drvdata *drvdata)
>   	write_trfcr(trfcr);
>   
>   	/* Set filters for guests and pass to KVM */
> -	if (drvdata->config.mode & ETM_MODE_EXCL_GUEST)
> +	if (config->mode & ETM_MODE_EXCL_GUEST)
>   		guest_trfcr = drvdata->trfcr & ~(TRFCR_EL1_ExTRE | TRFCR_EL1_E0TRE);
>   	else
>   		guest_trfcr = etm4x_get_kern_user_filter(drvdata);
> @@ -499,7 +505,7 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
>   {
>   	int i, rc;
>   	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 device *etm_dev = &csdev->dev;
>   	struct csdev_access *csa = &csdev->access;
> @@ -616,23 +622,46 @@ 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 = arg->config;
>   
> -	/* The tracer didn't start */
> +	if (arg->cfg_hash) {
> +		arg->rc = cscfg_csdev_enable_active_config(csdev,
> +							   arg->cfg_hash,
> +							   arg->preset);
> +		if (arg->rc)
> +			goto err;
> +	}
> +
> +	drvdata->trcid = arg->trace_id;
> +
> +	/* Tracer will never be paused in sysfs mode */
> +	drvdata->paused = false;
> +
> +	arg->rc = etm4_enable_hw(drvdata);
>   	if (arg->rc)
> -		coresight_set_mode(csdev, CS_MODE_DISABLED);
> +		goto err;
> +
> +	drvdata->sticky_enable = true;
> +
> +	return;
> +err:
> +	/* The tracer didn't start */
> +	etm4_release_trace_id(drvdata);

[NIT] better move this error handle to etm4_enable_sysfs.

smp_call_function_single possible return before call 
etm4_enable_sysfs_smp_call if the cpu is offline. The error path here 
cannot handle this error, breaking previous logic(handle all errors in 
etm4_enable_sysfs by releasing trace id).

There is no harm in not releasing the trace id here because ETM can 
re-use the allocated trace ID. But it's better to fix the inconsistent 
logic.

Thanks,
Jie

> +	coresight_set_mode(csdev, CS_MODE_DISABLED);
>   }
>   
>   /*
> @@ -670,7 +699,7 @@ 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 +783,7 @@ 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,
>   	};
> @@ -916,38 +945,24 @@ 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) {
> -			etm4_release_trace_id(drvdata);
> -			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;
> +
> +	raw_spin_lock(&drvdata->spinlock);
> +	arg.config = drvdata->config;
> +	raw_spin_unlock(&drvdata->spinlock);
> +
>   	ret = smp_call_function_single(drvdata->cpu,
>   				       etm4_enable_sysfs_smp_call, &arg, 1);
>   	if (!ret)
>   		ret = arg.rc;
> -	if (!ret)
> -		drvdata->sticky_enable = true;
> -
> -	if (ret)
> -		etm4_release_trace_id(drvdata);
> -
> -	raw_spin_unlock(&drvdata->spinlock);
> -
>   	if (!ret)
>   		dev_dbg(&csdev->dev, "ETM tracing enabled\n");
>   	return ret;
> @@ -1036,7 +1051,7 @@ 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;
> @@ -1072,6 +1087,8 @@ 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);
>   }
>   
> @@ -1122,7 +1139,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
>   	 * DYING hotplug callback is serviced by the ETM driver.
>   	 */
>   	cpus_read_lock();
> -	raw_spin_lock(&drvdata->spinlock);
>   
>   	/*
>   	 * Executing etm4_disable_hw on the cpu whose ETM is being disabled
> @@ -1131,10 +1147,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
>   	smp_call_function_single(drvdata->cpu, etm4_disable_sysfs_smp_call,
>   				 drvdata, 1);
>   
> -	raw_spin_unlock(&drvdata->spinlock);
> -
> -	cscfg_csdev_disable_active_config(csdev);
> -
>   	cpus_read_unlock();
>   
>   	/*
> @@ -1377,6 +1389,7 @@ 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;
> @@ -1384,6 +1397,7 @@ 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,
> @@ -1444,7 +1458,7 @@ 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);
>   	/*
> @@ -1689,7 +1703,7 @@ 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
> @@ -1730,7 +1744,7 @@ 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)
> @@ -1848,13 +1862,11 @@ static int etm4_starting_cpu(unsigned int cpu)
>   	if (!etmdrvdata[cpu])
>   		return 0;
>   
> -	raw_spin_lock(&etmdrvdata[cpu]->spinlock);
>   	if (!etmdrvdata[cpu]->os_unlock)
>   		etm4_os_unlock(etmdrvdata[cpu]);
>   
>   	if (coresight_get_mode(etmdrvdata[cpu]->csdev))
>   		etm4_enable_hw(etmdrvdata[cpu]);
> -	raw_spin_unlock(&etmdrvdata[cpu]->spinlock);
>   	return 0;
>   }
>   
> @@ -1863,10 +1875,8 @@ static int etm4_dying_cpu(unsigned int cpu)
>   	if (!etmdrvdata[cpu])
>   		return 0;
>   
> -	raw_spin_lock(&etmdrvdata[cpu]->spinlock);
>   	if (coresight_get_mode(etmdrvdata[cpu]->csdev))
>   		etm4_disable_hw(etmdrvdata[cpu]);
> -	raw_spin_unlock(&etmdrvdata[cpu]->spinlock);
>   	return 0;
>   }
>   
> @@ -2252,7 +2262,8 @@ 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 8864cfb76bad..725e6360a8b9 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -1071,6 +1071,7 @@ 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.
> @@ -1091,6 +1092,7 @@ 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);