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

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];