[PATCH v8 11/16] x86/resctrl: Add PMT registration API for AET enumeration callbacks

[Tony Luck <tony.luck@intel.com>]

resctrl is always built-in; INTEL_PMT_TELEMETRY may be a module.  Add, and
export, register/unregister functions so the PMT module can supply/clear
enumeration callback functions when loaded/unloaded.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---
v8:
	Add comment for what aet_register_lock will protect

 arch/x86/include/asm/resctrl.h          | 22 ++++++++++++++++
 arch/x86/kernel/cpu/resctrl/intel_aet.c | 34 +++++++++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index a9f481b7a8ed..48ad55bcda66 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -4,6 +4,8 @@
 
 #ifdef CONFIG_X86_CPU_RESCTRL
 
+#include <linux/intel_pmt_features.h>
+#include <linux/intel_vsec.h>
 #include <linux/jump_label.h>
 #include <linux/percpu.h>
 #include <linux/resctrl_types.h>
@@ -189,11 +191,31 @@ static inline void resctrl_arch_mon_ctx_free(struct rdt_resource *r,
 
 void resctrl_cpu_detect(struct cpuinfo_x86 *c);
 
+#ifdef CONFIG_X86_CPU_RESCTRL_INTEL_AET
+void intel_aet_register_enumeration(struct module *module,
+				    struct pmt_feature_group *(*get)(enum pmt_feature_id id),
+				    void (*put)(struct pmt_feature_group *p));
+void intel_aet_unregister_enumeration(void);
 #else
+static inline void intel_aet_register_enumeration(struct module *module,
+						  struct pmt_feature_group *(*get)(enum pmt_feature_id id),
+						  void (*put)(struct pmt_feature_group *p)) { }
+static inline void intel_aet_unregister_enumeration(void) { }
+#endif /* CONFIG_X86_CPU_RESCTRL_INTEL_AET */
+
+#else
+
+#include <linux/intel_pmt_features.h>
+#include <linux/intel_vsec.h>
 
 static inline void resctrl_arch_sched_in(struct task_struct *tsk) {}
 static inline void resctrl_cpu_detect(struct cpuinfo_x86 *c) {}
 
+static inline void intel_aet_register_enumeration(struct module *module,
+						  struct pmt_feature_group *(*get)(enum pmt_feature_id id),
+						  void (*put)(struct pmt_feature_group *p)) { }
+static inline void intel_aet_unregister_enumeration(void) { }
+
 #endif /* CONFIG_X86_CPU_RESCTRL */
 
 #endif /* _ASM_X86_RESCTRL_H */
diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
index 07e9d6d4959e..bc15cf37a7d0 100644
--- a/arch/x86/kernel/cpu/resctrl/intel_aet.c
+++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c
@@ -12,17 +12,21 @@
 #define pr_fmt(fmt)   "resctrl: " fmt
 
 #include <linux/bits.h>
+#include <linux/cleanup.h>
 #include <linux/compiler_types.h>
 #include <linux/container_of.h>
 #include <linux/cpumask.h>
 #include <linux/err.h>
 #include <linux/errno.h>
+#include <linux/export.h>
 #include <linux/gfp_types.h>
 #include <linux/init.h>
 #include <linux/intel_pmt_features.h>
 #include <linux/intel_vsec.h>
 #include <linux/io.h>
 #include <linux/minmax.h>
+#include <linux/mutex.h>
+#include <linux/module.h>
 #include <linux/printk.h>
 #include <linux/rculist.h>
 #include <linux/rcupdate.h>
@@ -291,6 +295,10 @@ static enum pmt_feature_id lookup_pfid(const char *pfname)
 	return FEATURE_INVALID;
 }
 
+static struct module *pmt_module;
+static struct pmt_feature_group *(*get_feature)(enum pmt_feature_id id);
+static void (*put_feature)(struct pmt_feature_group *p);
+
 /*
  * Request a copy of struct pmt_feature_group for each event group. If there is
  * one, the returned structure has an array of telemetry_region structures,
@@ -325,6 +333,32 @@ bool intel_aet_get_events(void)
 	return ret;
 }
 
+/*
+ * Defend against races between pmt_telemetry register/unregister and
+ * resctrl file system mount/unmount.
+ */
+static DEFINE_MUTEX(aet_register_lock);
+
+void intel_aet_register_enumeration(struct module *module,
+				    struct pmt_feature_group *(*get)(enum pmt_feature_id id),
+				    void (*put)(struct pmt_feature_group *p))
+{
+	guard(mutex)(&aet_register_lock);
+	get_feature = get;
+	put_feature = put;
+	pmt_module = module;
+}
+EXPORT_SYMBOL_NS_GPL(intel_aet_register_enumeration, "INTEL_PMT");
+
+void intel_aet_unregister_enumeration(void)
+{
+	guard(mutex)(&aet_register_lock);
+	pmt_module = NULL;
+	get_feature = NULL;
+	put_feature = NULL;
+}
+EXPORT_SYMBOL_NS_GPL(intel_aet_unregister_enumeration, "INTEL_PMT");
+
 void __exit intel_aet_exit(void)
 {
 	struct event_group **peg;
-- 
2.54.0