[PATCH v10 06/17] x86/resctrl: Drop global 'rdt_mon_capable' flag

[Tony Luck]

File system code calls resctrl_arch_mon_capable() to determine if the
system supports any monitoring features.

x86 architecture code sets a global flag to support implementation of
resctrl_arch_mon_capable() but the upcoming change to enumerate AET
(Application Energy Telemetry) features on each mount introduces a new
corner case.

Specifically when AET is the only monitoring feature, loading and
unloading the pmt_telemetry module between resctrl mounts may result
in monitoring support enabled on some mounts, but not on others.

Replace the global flag with a scan of resources to check if any are
marked mon_capable.

Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
---
v10:
	Move declaration of resctrl_arch_mon_capable() to <linux/resctrl.h>
	and provide kerneldoc comment on usage.

 include/linux/arm_mpam.h              |  1 -
 include/linux/resctrl.h               | 17 +++++++++++++++++
 arch/x86/include/asm/resctrl.h        |  6 ------
 arch/x86/kernel/cpu/resctrl/core.c    | 19 ++++++++++++++++---
 arch/x86/kernel/cpu/resctrl/monitor.c |  6 ------
 5 files changed, 33 insertions(+), 16 deletions(-)

diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
index f92a36187a52..b6e8683657c0 100644
--- a/include/linux/arm_mpam.h
+++ b/include/linux/arm_mpam.h
@@ -51,7 +51,6 @@ static inline int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
 #endif
 
 bool resctrl_arch_alloc_capable(void);
-bool resctrl_arch_mon_capable(void);
 
 void resctrl_arch_set_cpu_default_closid(int cpu, u32 closid);
 void resctrl_arch_set_closid_rmid(struct task_struct *tsk, u32 closid, u32 rmid);
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index a184500745f8..59ddedb27539 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -419,6 +419,23 @@ u32 resctrl_arch_get_num_closid(struct rdt_resource *r);
 u32 resctrl_arch_system_num_rmid_idx(void);
 int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid);
 
+/**
+ * resctrl_arch_mon_capable() - Report whether monitor events are enabled
+ *
+ * Some monitor events may be enumerated or implemented in loadable modules.
+ * This means that available events may vary from one mount of the resctrl
+ * file system to another. If modules are not loaded at mount time there
+ * may be no monitor events at all.
+ *
+ * File system code may call it during mount after architecture enumeration is
+ * complete. Calls during domain add/remove operations must check resctrl_mounted
+ * before calling.
+ *
+ * Return:
+ * true if any monitor events are enabled in the current mount cycle.
+ */
+bool resctrl_arch_mon_capable(void);
+
 /**
  * resctrl_enable_mon_event() - Enable monitoring event
  * @eventid:	ID of the event
diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index 575f8408a9e7..923b188e11a7 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -43,7 +43,6 @@ struct resctrl_pqr_state {
 DECLARE_PER_CPU(struct resctrl_pqr_state, pqr_state);
 
 extern bool rdt_alloc_capable;
-extern bool rdt_mon_capable;
 
 DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
 DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
@@ -66,11 +65,6 @@ static inline void resctrl_arch_disable_alloc(void)
 	static_branch_dec_cpuslocked(&rdt_enable_key);
 }
 
-static inline bool resctrl_arch_mon_capable(void)
-{
-	return rdt_mon_capable;
-}
-
 static inline void resctrl_arch_enable_mon(void)
 {
 	static_branch_enable_cpuslocked(&rdt_mon_enable_key);
diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index e3544c99cff1..fb20a31d8c73 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -51,6 +51,21 @@ DEFINE_PER_CPU(struct resctrl_pqr_state, pqr_state);
  */
 bool rdt_alloc_capable;
 
+/*
+ * Some monitor events depend on whether the module(s) that enumerate them
+ * are loaded. So resctrl must re-evaluate whether monitoring is supported
+ * for each mount.
+ */
+bool resctrl_arch_mon_capable(void)
+{
+	struct rdt_resource *r;
+
+	for_each_mon_capable_rdt_resource(r)
+		return true;
+
+	return false;
+}
+
 static void mba_wrmsr_intel(struct msr_param *m);
 static void cat_wrmsr(struct msr_param *m);
 static void mba_wrmsr_amd(struct msr_param *m);
@@ -780,7 +795,6 @@ void resctrl_arch_pre_mount(void)
 	cpus_read_lock();
 	mutex_lock(&domain_list_lock);
 	r->mon_capable = true;
-	rdt_mon_capable = true;
 	for_each_online_cpu(cpu)
 		domain_add_cpu_mon(cpu, r);
 	mutex_unlock(&domain_list_lock);
@@ -1014,9 +1028,8 @@ static __init void check_quirks(void)
 static __init bool get_rdt_resources(void)
 {
 	rdt_alloc_capable = get_rdt_alloc_resources();
-	rdt_mon_capable = get_rdt_mon_resources();
 
-	return (rdt_mon_capable || rdt_alloc_capable);
+	return get_rdt_mon_resources() || rdt_alloc_capable;
 }
 
 static __init void rdt_init_res_defs_intel(void)
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 430b8fae0b77..1fea893f2cc1 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -26,12 +26,6 @@
 
 #include "internal.h"
 
-/*
- * Global boolean for rdt_monitor which is true if any
- * resource monitoring is enabled.
- */
-bool rdt_mon_capable;
-
 #define CF(cf)	((unsigned long)(1048576 * (cf) + 0.5))
 
 static int snc_nodes_per_l3_cache = 1;
-- 
2.55.0