[PATCH v8 08/13] coresight: etm4x: fix inconsistencies with sysfs configuration
Suzuki K Poulose
suzuki.poulose at arm.com
Thu Jul 16 05:46:23 PDT 2026
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 at 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];
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