Re: [PATCH v8 08/13] coresight: etm4x: fix inconsistencies with sysfs configuration

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 29/06/2026 10:00, 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.
> 
> Fixes: 54ff892b76c6 ("coresight: etm4x: splitting struct etmv4_drvdata")
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>   .../hwtracing/coresight/coresight-etm4x-cfg.c |   2 +-
>   .../coresight/coresight-etm4x-core.c          | 103 ++++++++++--------
>   drivers/hwtracing/coresight/coresight-etm4x.h |   2 +
>   3 files changed, 58 insertions(+), 49 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> index 9b4947d75fde..9d56e17e09b1 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 2798604943ed..31ac7783fdb8 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -245,6 +245,7 @@ void etm4_release_trace_id(struct etmv4_drvdata *drvdata)
>   struct etm4_enable_arg {
>   	struct etmv4_drvdata *drvdata;
>   	struct coresight_path *path;
> +	struct etmv4_config config;
>   	int rc;
>   };
>   
> @@ -270,10 +271,11 @@ 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 +283,7 @@ 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 +294,13 @@ 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 +308,7 @@ 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 +502,7 @@ 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;
> @@ -619,27 +622,52 @@ 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;
> +	unsigned long cfg_hash;
> +	int preset;
>   
>   	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;

I see, we copy the sysfs config to init_arg and then apply it here.

>   
> -	/* The tracer didn't start */
> +	/* enable any config activated by configfs */
> +	cscfg_config_sysfs_get_active_cfg(&cfg_hash, &preset);
> +	if (cfg_hash) {
> +		arg->rc = cscfg_csdev_enable_active_config(csdev,
> +							   cfg_hash,
> +							   preset);
> +		if (arg->rc)
> +			goto err;
> +	}
> +
> +	drvdata->trcid = arg->path->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);
> -		return;
> +		cscfg_csdev_disable_active_config(csdev);
> +		goto err;
>   	}
>   
> +	drvdata->sticky_enable = true;
>   	csdev->path = arg->path;
> +
> +	return;
> +err:
> +	/* The tracer didn't start */
> +	coresight_set_mode(csdev, CS_MODE_DISABLED);

Do we need to reset the active_config ?


> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index c0f7da17a186..a974e4d05838 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -1068,6 +1068,7 @@ 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.

Please could you update the documentation for "config" -> holding sysfs 
mode configuration.

Suzuki


>    * @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;
>   	u32				ss_status[ETM_MAX_SS_CMP];