Re: [PATCH v11 3/9] coresight: etm4x: fix inconsistencies with sysfs configuration

On Fri, Sep 18, 2026 at 02:49:09PM +0100, Mike Leach wrote:

Hi,

On 9/15/26 12:34, 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

I'll add a comment about naming here - active_config is a bit overloaded in the code as it is also used by the csconfig code to represent a loaded and active configuration - which may at some point be applied to the active_config above.

If active_config is for the current session then curr_config would work.

Additionally config also appears as a local pointer in many of the functions. If this is the sysfs config then sysfs_config would work better.

This should make all the code a lot more readable, and easier to spot exactly which config we are dealing with.

Okay. then I'll change the each name with curr_config and sysfs_config and rename all.

Thanks ;)

...

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.

As the active_config is used for cfg-configfs, etmv4 doesn't need to set its lock for the cfg-configfs since the active_config is proceted by cs_mode otherwise it would make a possible cpu-stall when it get interrupt while setting the sysfs configuration.

Therefore, set the drv_spinlock for cfg-configfs as NULL and let the cfg-configfs disable irq without grap drv_spinlock when it is NULL.

Fixes: 54ff892b76c6 ("coresight: etm4x: splitting struct etmv4_drvdata") Signed-off-by: Yeoreum Yun yeoreum.yun@arm.com

---

drivers/hwtracing/coresight/coresight-config.c | 18 ++-- drivers/hwtracing/coresight/coresight-config.h | 22 ++++ drivers/hwtracing/coresight/coresight-etm4x-cfg.c | 13 ++- drivers/hwtracing/coresight/coresight-etm4x-core.c | 118 ++++++++++++--------- .../hwtracing/coresight/coresight-etm4x-sysfs.c | 6 +- drivers/hwtracing/coresight/coresight-etm4x.h | 4 +- 6 files changed, 113 insertions(+), 68 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-config.c b/drivers/hwtracing/coresight/coresight-config.c index 4f72ae71b696e..0e296289f286d 100644 --- a/drivers/hwtracing/coresight/coresight-config.c +++ b/drivers/hwtracing/coresight/coresight-config.c @@ -73,13 +73,12 @@ static void cscfg_init_reg_param(struct cscfg_feature_csdev *feat_csdev, /* set values into the driver locations referenced in cscfg_reg_csdev */ static int cscfg_set_on_enable(struct cscfg_feature_csdev *feat_csdev) {

• unsigned long flags; int i;
• raw_spin_lock_irqsave(feat_csdev->drv_spinlock, flags);
• for (i = 0; i < feat_csdev->nr_regs; i++)

• cscfg_set_reg(&feat_csdev->regs_csdev[i]);
  

• raw_spin_unlock_irqrestore(feat_csdev->drv_spinlock, flags);

• scoped_guard(feat_csdev_lock, feat_csdev) {

• for (i = 0; i < feat_csdev->nr_regs; i++)
  

• 	cscfg_set_reg(&feat_csdev->regs_csdev[i]);
  

• } dev_dbg(&feat_csdev->csdev->dev, "Feature %s: %s", feat_csdev->feat_desc->name, "set on enable"); return 0;

@@ -88,13 +87,12 @@ static int cscfg_set_on_enable(struct cscfg_feature_csdev *feat_csdev) /* copy back values from the driver locations referenced in cscfg_reg_csdev */ static void cscfg_save_on_disable(struct cscfg_feature_csdev *feat_csdev) {

• unsigned long flags; int i;
• raw_spin_lock_irqsave(feat_csdev->drv_spinlock, flags);
• for (i = 0; i < feat_csdev->nr_regs; i++)

• cscfg_save_reg(&feat_csdev->regs_csdev[i]);
  

• raw_spin_unlock_irqrestore(feat_csdev->drv_spinlock, flags);

• scoped_guard(feat_csdev_lock, feat_csdev) {

• for (i = 0; i < feat_csdev->nr_regs; i++)
  

• 	cscfg_save_reg(&feat_csdev->regs_csdev[i]);
  

• } dev_dbg(&feat_csdev->csdev->dev, "Feature %s: %s", feat_csdev->feat_desc->name, "save on disable"); }

diff --git a/drivers/hwtracing/coresight/coresight-config.h b/drivers/hwtracing/coresight/coresight-config.h index 90fd937d3bd83..ae6295e308131 100644 --- a/drivers/hwtracing/coresight/coresight-config.h +++ b/drivers/hwtracing/coresight/coresight-config.h @@ -7,6 +7,7 @@ #ifndef _CORESIGHT_CORESIGHT_CONFIG_H #define _CORESIGHT_CORESIGHT_CONFIG_H +#include <linux/cleanup.h> #include <linux/coresight.h> #include <linux/types.h> @@ -259,4 +260,25 @@ void cscfg_csdev_disable_config(struct cscfg_config_csdev *config_csdev); /* reset a feature to default values */ void cscfg_reset_feat(struct cscfg_feature_csdev *feat_csdev); +#define feat_csdev_lock(feat_csdev, flags) \

• do { \

• raw_spinlock_t *__lock = feat_csdev->drv_spinlock;	\
  

• typecheck(unsigned long, flags);			\
  

• if (__lock)						\
  

• 	raw_spin_lock_irqsave(__lock, flags);		\
  

• } while (0)

+#define feat_csdev_unlock(feat_csdev, flags) \

• do { \

• raw_spinlock_t *__lock = feat_csdev->drv_spinlock;	\
  

• typecheck(unsigned long, flags);			\
  

• if (__lock)						\
  

• 	raw_spin_unlock_irqrestore(__lock, flags);	\
  

• } while (0)

+DEFINE_LOCK_GUARD_1(feat_csdev_lock, struct cscfg_feature_csdev,

•     feat_csdev_lock(_T->lock, _T->flags),
  

•     feat_csdev_unlock(_T->lock, _T->flags),
  

•     unsigned long flags)
  

• #endif /* _CORESIGHT_CORESIGHT_CONFIG_H */

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c index e1a59b4345052..d24f533c623d0 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)) ||

@@ -154,11 +154,14 @@ static int etm4_cfg_load_feature(struct coresight_device *csdev, int i = 0, err = 0; /*

• * essential we set the device spinlock - this is used in the generic
  

• * programming routines when copying values into the drvdata structures
  

• * via the pointers setup in etm4_cfg_map_reg_offset().
  

• * drvdata structure of etm4 for configfs is active_config and
  

• * this active_config is protected with csdev->mode by restricting
  

• * access to active_config after mode changed to PERF or SYSFS.
  

• *
  

• * Therefore, it doesn't need to protected with etmv4_drvdata->spinlock
  

• * to feature applying and set the NULL.
  

  */

• feat_csdev->drv_spinlock = &drvdata->spinlock;

• feat_csdev->drv_spinlock = NULL; /* process the register descriptions */ for (i = 0; i < feat_csdev->nr_regs && !err; i++) {

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c index 2247ad55d4442..2df7f592bb5cf 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c @@ -239,6 +239,7 @@ 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;

drvdata contains both active_config and config - why the extra copy here?

This is because of a minor consistency before applying the configuration to hardware. Since drvdata->sysfs_config could be modified while copying the contents into the active_config as a purpose of snapshot at the time of enable, add this argument.

For example, while enabling, sysfs could modify the ctxid_mask0 and ctxid_mask1 and this could be teared when active_config is copied from drvdata->config directly.

Therefore, make a config as a *snapshot* while holding a drvdata->lock. otherwise, we need to change all spinlock usage in sysfs should be irqsave but it seems much awful.

But I think we can remove it if we move the copy config to active_config into etm4_enable_sysfs() since there, sysfs_mode is taken. so active_config could be accessed safely.

I'll move the drvdata->active_config = drvdata->config into etm4_enable_sysfs() and will remove this arg.

Thanks!

...

int rc; }; @@ -264,10 +265,11 @@ 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;

@@ -275,7 +277,7 @@ 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

@@ -286,12 +288,13 @@ 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);

@@ -299,7 +302,7 @@ 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);

@@ -492,7 +495,7 @@ static int etm4_enable_trace_unit(struct etmv4_drvdata *drvdata) static int etm4_enable_hw(struct etmv4_drvdata *drvdata) { int i, rc;

• 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;

@@ -612,27 +615,44 @@ 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;
• if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {

• /* Someone is already using the tracer */
  

• arg->rc = -EBUSY;
  

• return;
  

• drvdata = arg->drvdata;
• csdev = drvdata->csdev;
• drvdata->active_config = arg->config;

This can happen before the smp call removing the need for arg->config?

Yes! That's fair enough :)

...

• /* 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)
  

• 	return;
  

  }

• arg->rc = etm4_enable_hw(arg->drvdata);

• drvdata->trcid = arg->path->trace_id;

• /* The tracer didn't start */

• /* 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);
  

• cscfg_csdev_disable_active_config(csdev);
  

  return; }
• drvdata->sticky_enable = true; csdev->path = arg->path;
• return; } /*

@@ -669,7 +689,7 @@ static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata, { int ctridx; int rselector;

• 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 (!drvdata->nr_cntr)

@@ -752,7 +772,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev, { int ret = 0; struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);

• 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, };

@@ -919,46 +939,36 @@ static int etm4_enable_sysfs(struct coresight_device *csdev, struct coresight_pa { struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent); struct etm4_enable_arg arg = { };

• unsigned long cfg_hash;
• int ret, preset;

• int ret;

• /* 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;
  

• }
  

• if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {

• /* Someone is already using the tracer */
  

• return -EBUSY;
  

  }

• 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.path = path;

• scoped_guard(raw_spinlock, &drvdata->spinlock) {

• arg.config = drvdata->config;
  

Given as mentioned above that once a mode is set then active_config is protected, this should simply be drvdata->active_config = drvdata->config; ??

Right. Here is much better!

...

• }
• 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)

• if (!ret) {

• dev_dbg(&csdev->dev, "ETM tracing enabled\n");
  

• } else { etm4_release_trace_id(drvdata);

• /* The tracer didn't start */
  

• coresight_set_mode(csdev, CS_MODE_DISABLED);
  

• }

• raw_spin_unlock(&drvdata->spinlock);
• if (!ret)

• dev_dbg(&csdev->dev, "ETM tracing enabled\n");
  

  return ret; }

@@ -1044,7 +1054,7 @@ static void etm4_disable_trace_unit(struct etmv4_drvdata *drvdata) static void etm4_disable_hw(struct etmv4_drvdata *drvdata) { u32 control;

• 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;

@@ -1086,8 +1096,9 @@ static void etm4_disable_sysfs_smp_call(void *info) etm4_disable_hw(drvdata);

• cscfg_csdev_disable_active_config(drvdata->csdev);
• drvdata->csdev->path = NULL;

• coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED); } static int etm4_disable_perf(struct coresight_device *csdev,

@@ -1130,8 +1141,9 @@ static int etm4_disable_perf(struct coresight_device *csdev, static void etm4_disable_sysfs(struct coresight_device *csdev) { struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);

• raw_spin_lock(&drvdata->spinlock);

• struct etmv4_config *config = &drvdata->config;
• const struct etmv4_config *active_config = &drvdata->active_config;
• int i; /*
  • Executing etm4_disable_hw on the cpu whose ETM is being disabled

@@ -1140,9 +1152,17 @@ 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);

• /*

• * Userspace may read ss_status and cntr_val through sysfs after
  

• * the sysfs-session has been disabled.
  

• */
  

• for (i = 0; i < drvdata->nr_ss_cmp; i++)

• config->ss_status[i] = active_config->ss_status[i];
  

• cscfg_csdev_disable_active_config(csdev);

• for (i = 0; i < drvdata->nr_cntr; i++)

• config->cntr_val[i] = active_config->cntr_val[i];
  

Readback of TRCSEQSTR needed here too.

Right. I've noticted after I post this patch. I'll fix in the next version. Thanks!

...

• coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED); /*
  • we only release trace IDs when resetting sysfs.

@@ -1690,7 +1710,7 @@ 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

@@ -1731,7 +1751,7 @@ 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)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c index 8d73248b840a6..f64c0acebc701 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c @@ -1613,7 +1613,7 @@ static ssize_t cntr_val_store(struct device *dev, return -EINVAL; if (val > ETM_CNTR_MAX_VAL) return -EINVAL;

• if (coresight_get_mode(drvdata->csdev))

• if (coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS) return -EBUSY; raw_spin_lock(&drvdata->spinlock);

@@ -1799,7 +1799,7 @@ static ssize_t sshot_ctrl_store(struct device *dev, if (kstrtoul(buf, 16, &val)) return -EINVAL;

• if (coresight_get_mode(drvdata->csdev))

• if (coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS) return -EBUSY; raw_spin_lock(&drvdata->spinlock);

@@ -1851,7 +1851,7 @@ static ssize_t sshot_pe_ctrl_store(struct device *dev, if (kstrtoul(buf, 16, &val)) return -EINVAL;

• if (coresight_get_mode(drvdata->csdev))

• if (coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS) return -EBUSY; raw_spin_lock(&drvdata->spinlock);

diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h index df9e0748d71ec..c33700711154d 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x.h +++ b/drivers/hwtracing/coresight/coresight-etm4x.h @@ -1019,7 +1019,8 @@ 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.
  

• • @config: structure holding configuration parameters.

• • @active_config: structure holding current applied configuration.
• • @config: structure holding sysfs mode configuration.
  • @save_state: State to be preserved across power loss
  • @skip_power_up: Indicates if an implementation can skip powering up

  •    the trace unit.
    

@@ -1077,6 +1078,7 @@ struct etmv4_drvdata { bool skip_power_up : 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);

Regards

Mike

Thanks!