Enumeration of Intel telemetry events is not complete when the
resctrl "late_init" code is executed.

Add a hook at the beginning of the mount code that will be used
to check for telemetry events and initialize if any are found.

The hook is called on every attempted mount. But expectations are that
most actions (like enumeration) will only need to be performed
on the first call.

The call is made with no locks held. Architecture code is responsible
for any required locking.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 include/linux/resctrl.h            | 6 ++++++
 arch/x86/kernel/cpu/resctrl/core.c | 9 +++++++++
 fs/resctrl/rdtgroup.c              | 2 ++
 3 files changed, 17 insertions(+)

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index e9a1cabfc724..d2fc0fcd0226 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -460,6 +460,12 @@ void resctrl_offline_mon_domain(struct rdt_resource *r, struct rdt_domain_hdr *h
 void resctrl_online_cpu(unsigned int cpu);
 void resctrl_offline_cpu(unsigned int cpu);
 
+/*
+ * Architecture hook called for each attempted file system mount.
+ * No locks are held.
+ */
+void resctrl_arch_pre_mount(void);
+
 /**
  * resctrl_arch_rmid_read() - Read the eventid counter corresponding to rmid
  *			      for this resource and domain.
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 0286d3cf6754..22ff91b666d0 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -717,6 +717,15 @@ static int resctrl_arch_offline_cpu(unsigned int cpu)
 	return 0;
 }
 
+void resctrl_arch_pre_mount(void)
+{
+	static atomic_t only_once = ATOMIC_INIT(0);
+	int old = 0;
+
+	if (!atomic_try_cmpxchg(&only_once, &old, 1))
+		return;
+}
+
 enum {
 	RDT_FLAG_CMT,
 	RDT_FLAG_MBM_TOTAL,
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 6df06bf0e694..627243a1175c 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -2585,6 +2585,8 @@ static int rdt_get_tree(struct fs_context *fc)
 	struct rdt_resource *r;
 	int ret;
 
+	resctrl_arch_pre_mount();
+
 	cpus_read_lock();
 	mutex_lock(&rdtgroup_mutex);
 	/*
-- 
2.50.0

Hi Tony,

On 7/11/25 4:53 PM, Tony Luck wrote:
> Enumeration of Intel telemetry events is not complete when the
> resctrl "late_init" code is executed.

Could you please expand the context to provide detail on why
this enumeration is not complete at resctrl init time? What guarantee
is there that the enumeration will be complete at resctrl mount time?

> 
> Add a hook at the beginning of the mount code that will be used
> to check for telemetry events and initialize if any are found.
> 
> The hook is called on every attempted mount. But expectations are that

"Call the hook ..." (I do not think I need to point these out anymore,
will leave to you to rework all changelogs)

> most actions (like enumeration) will only need to be performed
> on the first call.
> 
> The call is made with no locks held. Architecture code is responsible
> for any required locking.
> 
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> ---
>  include/linux/resctrl.h            | 6 ++++++
>  arch/x86/kernel/cpu/resctrl/core.c | 9 +++++++++
>  fs/resctrl/rdtgroup.c              | 2 ++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index e9a1cabfc724..d2fc0fcd0226 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -460,6 +460,12 @@ void resctrl_offline_mon_domain(struct rdt_resource *r, struct rdt_domain_hdr *h
>  void resctrl_online_cpu(unsigned int cpu);
>  void resctrl_offline_cpu(unsigned int cpu);
>  
> +/*
> + * Architecture hook called for each attempted file system mount.

"for each attempted file system mount" -> "at beginning of each file system mount attempt"?

Reinette