[PATCH v14 20/24] x86/resctrl: Export interface to report telemetry unbind/remove

[Tony Luck]

resctrl obtains the addresses of the telemetry MMIO regions from the
pmt_telemetry driver at mount time and holds a reference on the module
until unmount, so the module cannot be unloaded while resctrl may read
the counters.

The module reference does not prevent a telemetry device from being
unbound from the driver, or removed. Either tears down the MMIO mappings
that hold the event counters, and a subsequent read of an event by
resctrl faults on the stale address.

Provide an interface for pmt_telemetry to report that the mappings for a
package are about to be torn down. Stop using the regions of that package
and serialize event reads with the notification so that no read uses an
address once it has been reported. Events of the affected package then
read "Unavailable".

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
v14:
	Dropped aet_mmio_lock. Now safe to use aet_lock.
	New commit message
	Add code comment noting that per-package may be over-reaction.
---
 include/linux/intel_vsec.h              |  2 ++
 arch/x86/kernel/cpu/resctrl/intel_aet.c | 30 +++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/linux/intel_vsec.h b/include/linux/intel_vsec.h
index c04b1d0f3143..bcbf4937c71c 100644
--- a/include/linux/intel_vsec.h
+++ b/include/linux/intel_vsec.h
@@ -262,11 +262,13 @@ 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);
+void intel_aet_invalidate(u8 package_id);
 #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) { }
+static inline void intel_aet_invalidate(u8 package_id) { }
 #endif /* CONFIG_X86_CPU_RESCTRL_INTEL_AET */
 
 #endif
diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
index 5c88236d850f..3facb852f22b 100644
--- a/arch/x86/kernel/cpu/resctrl/intel_aet.c
+++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c
@@ -339,6 +339,7 @@ static enum pmt_feature_id lookup_pfid(const char *pfname)
  * Serialises AET's view of pmt_telemetry:
  *   - pmt_module, get_feature, put_feature, pmt_in_use
  *   - every event_group's ->pfg
+ *   - the telemetry_region::addr entries reachable through ->pfg
  *
  * Lock ordering with pmt/telemetry.c's ep_lock is ep_lock -> aet_lock.
  * AET therefore must not call get_feature() (which takes ep_lock) while
@@ -413,6 +414,33 @@ void intel_aet_unregister_enumeration(void)
 }
 EXPORT_SYMBOL_NS_GPL(intel_aet_unregister_enumeration, "INTEL_PMT");
 
+/*
+ * pmt_telemetry driver calls while holding ep_lock. This is for unbind/remove
+ * operations that will invalidate the virtual addresses of MMIO registers
+ * provided by intel_pmt_get_regions_by_feature(). This simple interface may
+ * be overly broad if there are multiple telemetry devices per-package. An
+ * unbind/remove operation on one device will stop resctrl from reading
+ * event counters from all devices on the same package.
+ */
+void intel_aet_invalidate(u8 package_id)
+{
+	struct event_group **peg;
+
+	guard(mutex)(&aet_lock);
+
+	for_each_event_group(peg) {
+		struct event_group *e = *peg;
+
+		if (!e->pfg)
+			continue;
+		for (int i = 0; i < e->pfg->count; i++) {
+			if (e->pfg->regions[i].plat_info.package_id == package_id)
+				e->pfg->regions[i].addr = NULL;
+		}
+	}
+}
+EXPORT_SYMBOL_NS_GPL(intel_aet_invalidate, "INTEL_PMT");
+
 bool intel_aet_pre_mount(void)
 {
 	struct pmt_feature_group *(*get)(enum pmt_feature_id id);
@@ -488,6 +516,8 @@ int intel_aet_read_event(int domid, u32 rmid, void *arch_priv, u64 *val)
 	void *pevt0;
 	u32 idx;
 
+	guard(mutex)(&aet_lock);
+
 	pevt0 = pevt - pevt->idx;
 	e = container_of(pevt0, struct event_group, evts);
 	idx = rmid * e->num_events;
-- 
2.56.0