[PATCH v6 07/10] x86/resctrl: Resolve INTEL_PMT_TELEMETRY symbols at runtime

Tony Luck
2026-04-29T18:49:18Z

resctrl is always built-in, but INTEL_PMT_TELEMETRY and INTEL_TPMI are
logically independent and should be loadable modules. Switch AET to use
the function-pointer registration API (introduced in the preceding patch)
instead of direct link-time references to PMT symbols.

Move AET enumeration into resctrl_arch_pre_mount() and cleanup into
resctrl_arch_unmount() so the PMT module can be unloaded whenever the
filesystem is not mounted. Because all cleanup now happens in the unmount
path, intel_aet_exit() is no longer needed and is removed.

Note that the Linux file system code does not serialize calls to
fs_context_operations::get_tree(), so there may be arbitrarily many
parallel calls if users invoke mount(2) multiple times.

Add locking and state (resctrl_arch_mount_entries) to only perform enumeration
of first mount, and cleanup on last unmount.

event_group::num_rmid may be reset (reduced) during enumeration. This is
not worth resetting on unmount because the same reduction would occur on
each subsequent mount.

Signed-off-by: Tony Luck <tony.luck@intel.com>
---
include/linux/resctrl.h | 3 ++
arch/x86/kernel/cpu/resctrl/internal.h | 8 ++---
arch/x86/kernel/cpu/resctrl/core.c | 41 +++++++++++++++++++++++--
arch/x86/kernel/cpu/resctrl/intel_aet.c | 26 ++++++++++++----
4 files changed, 65 insertions(+), 13 deletions(-)

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 3705f0214fa6..9534d42e0c57 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -557,6 +557,9 @@ void resctrl_offline_cpu(unsigned int cpu);
*/
void resctrl_arch_pre_mount(void);

+/* Called to report unmount. */
+void resctrl_arch_unmount(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/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 3b09cfe9a046..017a19143ec9 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -234,15 +234,15 @@ void rdt_domain_reconfigure_cdp(struct rdt_resource *r);
void resctrl_arch_mbm_cntr_assign_set_one(struct rdt_resource *r);

#ifdef CONFIG_X86_CPU_RESCTRL_INTEL_AET
-bool intel_aet_get_events(void);
-void __exit intel_aet_exit(void);
+bool intel_aet_pre_mount(void);
+void intel_aet_unmount(void);
int intel_aet_read_event(int domid, u32 rmid, void *arch_priv, u64 *val);
void intel_aet_mon_domain_setup(int cpu, int id, struct rdt_resource *r,
struct list_head *add_pos);
bool intel_handle_aet_option(bool force_off, char *tok);
#else
-static inline bool intel_aet_get_events(void) { return false; }
-static inline void __exit intel_aet_exit(void) { }
+static inline bool intel_aet_pre_mount(void) { return false; }
+static inline void intel_aet_unmount(void) { }
static inline int intel_aet_read_event(int domid, u32 rmid, void *arch_priv, u64 *val)
{
return -EINVAL;
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 934492c7e643..9336299b9647 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -16,10 +16,12 @@

#define pr_fmt(fmt) "resctrl: " fmt

+#include <linux/cleanup.h>
#include <linux/cpu.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/cpuhotplug.h>
+#include <linux/mutex.h>

#include <asm/cpu_device_id.h>
#include <asm/msr.h>
@@ -776,12 +778,20 @@ static int resctrl_arch_offline_cpu(unsigned int cpu)
return 0;
}

+static DEFINE_MUTEX(resctrl_arch_mount_lock);
+static int resctrl_arch_mount_entries;
+
void resctrl_arch_pre_mount(void)
{
struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_PERF_PKG].r_resctrl;
int cpu;

- if (!intel_aet_get_events())
+ guard(mutex)(&resctrl_arch_mount_lock);
+
+ if (++resctrl_arch_mount_entries > 1)
+ return;
+
+ if (!intel_aet_pre_mount())
return;

/*
@@ -798,6 +808,33 @@ void resctrl_arch_pre_mount(void)
cpus_read_unlock();
}

+void resctrl_arch_unmount(void)
+{
+ struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_PERF_PKG].r_resctrl;
+ int cpu;
+
+ guard(mutex)(&resctrl_arch_mount_lock);
+
+ if (--resctrl_arch_mount_entries > 0)
+ return;
+
+ WARN_ON(resctrl_arch_mount_entries < 0);
+
+ intel_aet_unmount();
+
+ if (!r->mon_capable)
+ return;
+
+ cpus_read_lock();
+ mutex_lock(&domain_list_lock);
+ for_each_online_cpu(cpu)
+ domain_remove_cpu_mon(cpu, r);
+ r->mon_capable = false;
+ rdt_mon_feature_count--;
+ mutex_unlock(&domain_list_lock);
+ cpus_read_unlock();
+}
+
enum {
RDT_FLAG_CMT,
RDT_FLAG_MBM_TOTAL,
@@ -1174,8 +1211,6 @@ late_initcall(resctrl_arch_late_init);

static void __exit resctrl_arch_exit(void)
{
- intel_aet_exit();
-
cpuhp_remove_state(rdt_online);

resctrl_exit();
diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
index 2b3677783427..6e7458a722f9 100644
--- a/arch/x86/kernel/cpu/resctrl/intel_aet.c
+++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c
@@ -25,8 +25,8 @@
#include <linux/intel_vsec.h>
#include <linux/io.h>
#include <linux/minmax.h>
-#include <linux/mutex.h>
#include <linux/module.h>
+#include <linux/mutex.h>
#include <linux/printk.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
@@ -307,7 +307,7 @@ static void (*put_feature)(struct pmt_feature_group *p);
* struct pmt_feature_group to indicate that its events are successfully
* enabled.
*/
-bool intel_aet_get_events(void)
+static bool aet_get_events(void)
{
struct pmt_feature_group *p;
enum pmt_feature_id pfid;
@@ -316,14 +316,14 @@ bool intel_aet_get_events(void)

for_each_event_group(peg) {
pfid = lookup_pfid((*peg)->pfname);
- p = intel_pmt_get_regions_by_feature(pfid);
+ p = get_feature(pfid);
if (IS_ERR_OR_NULL(p))
continue;
if (enable_events(*peg, p)) {
(*peg)->pfg = p;
ret = true;
} else {
- intel_pmt_put_feature_group(p);
+ put_feature(p);
}
}

@@ -349,13 +349,27 @@ void intel_aet_unregister_enumeration(void)
}
EXPORT_SYMBOL_GPL(intel_aet_unregister_enumeration);

-void __exit intel_aet_exit(void)
+bool intel_aet_pre_mount(void)
+{
+ guard(mutex)(&aet_register_lock);
+ if (!get_feature || !put_feature)
+ return false;
+
+ return aet_get_events();
+}
+
+void intel_aet_unmount(void)
{
struct event_group **peg;

+ guard(mutex)(&aet_register_lock);
for_each_event_group(peg) {
if ((*peg)->pfg) {
- intel_pmt_put_feature_group((*peg)->pfg);
+ struct event_group *e = *peg;
+
+ for (int j = 0; j < e->num_events; j++)
+ resctrl_disable_mon_event(e->evts[j].id);
+ put_feature((*peg)->pfg);
(*peg)->pfg = NULL;
}
}
--
2.53.0