linux-kernel - [RFC PATCH 1/7] x86/resctrl: Add register/unregister functions for driver to hook into resctrl

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Date:   Thu, 20 Apr 2023 15:06:30 -0700
From:   Tony Luck <tony.luck@...el.com>
To:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Shaopeng Tan <tan.shaopeng@...itsu.com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        James Morse <james.morse@....com>,
        Babu Moger <babu.moger@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>
Subject: [RFC PATCH 1/7] x86/resctrl: Add register/unregister functions for driver to hook into resctrl

Just one callback at the point for the driver to be notified when the
resctrl filesystem is mounted or unmounted. Virtually all drivers
will need this hook to enable/disable their feature(s) as part of
mount/unmount.

Signed-off-by: Tony Luck <tony.luck@...el.com>
---
 include/linux/resctrl.h                | 13 +++++++
 arch/x86/kernel/cpu/resctrl/rdtgroup.c | 50 ++++++++++++++++++++++++++
 2 files changed, 63 insertions(+)

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 8334eeacfec5..78513edddca0 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -204,6 +204,19 @@ struct resctrl_schema {
 	u32				num_closid;
 };
 
+/**
+ * struct resctrl_driver - interface for driver to attach to resctrl
+ * @list:	List of registered drivers
+ * @mount:	Callback for mount/unmount
+ */
+struct resctrl_driver {
+	struct list_head	list;
+	void			(*mount)(bool mount);
+};
+
+int resctrl_register_driver(struct resctrl_driver *d);
+void resctrl_unregister_driver(struct resctrl_driver *d);
+
 /* The number of closid supported by this resource regardless of CDP */
 u32 resctrl_arch_get_num_closid(struct rdt_resource *r);
 int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid);
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 6ad33f355861..3e6778bde427 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -51,6 +51,9 @@ static struct kernfs_node *kn_mongrp;
 /* Kernel fs node for "mon_data" directory under root */
 static struct kernfs_node *kn_mondata;
 
+static LIST_HEAD(drivers);
+static bool resctrl_is_mounted;
+
 static struct seq_buf last_cmd_status;
 static char last_cmd_status_buf[512];
 
@@ -2437,6 +2440,42 @@ static int schemata_list_create(void)
 	return ret;
 }
 
+static void driver_up(struct resctrl_driver *d)
+{
+	if (d->mount)
+		d->mount(true);
+}
+
+static void driver_down(struct resctrl_driver *d)
+{
+	if (d->mount)
+		d->mount(false);
+}
+
+int resctrl_register_driver(struct resctrl_driver *d)
+{
+	mutex_lock(&rdtgroup_mutex);
+	list_add(&d->list, &drivers);
+
+	if (resctrl_is_mounted)
+		driver_up(d);
+	mutex_unlock(&rdtgroup_mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(resctrl_register_driver);
+
+void resctrl_unregister_driver(struct resctrl_driver *d)
+{
+	mutex_lock(&rdtgroup_mutex);
+	list_del(&d->list);
+
+	if (resctrl_is_mounted)
+		driver_down(d);
+	mutex_unlock(&rdtgroup_mutex);
+}
+EXPORT_SYMBOL_GPL(resctrl_unregister_driver);
+
 static void schemata_list_destroy(void)
 {
 	struct resctrl_schema *s, *tmp;
@@ -2450,6 +2489,7 @@ static void schemata_list_destroy(void)
 static int rdt_get_tree(struct fs_context *fc)
 {
 	struct rdt_fs_context *ctx = rdt_fc2context(fc);
+	struct resctrl_driver *d;
 	struct rdt_domain *dom;
 	struct rdt_resource *r;
 	int ret;
@@ -2516,6 +2556,10 @@ static int rdt_get_tree(struct fs_context *fc)
 			mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL);
 	}
 
+	list_for_each_entry(d, &drivers, list)
+		driver_up(d);
+	resctrl_is_mounted = true;
+
 	goto out;
 
 out_psl:
@@ -2761,6 +2805,7 @@ static void rmdir_all_sub(void)
 
 static void rdt_kill_sb(struct super_block *sb)
 {
+	struct resctrl_driver *d;
 	struct rdt_resource *r;
 
 	cpus_read_lock();
@@ -2780,6 +2825,11 @@ static void rdt_kill_sb(struct super_block *sb)
 	static_branch_disable_cpuslocked(&rdt_mon_enable_key);
 	static_branch_disable_cpuslocked(&rdt_enable_key);
 	kernfs_kill_sb(sb);
+
+	list_for_each_entry(d, &drivers, list)
+		driver_down(d);
+	resctrl_is_mounted = false;
+
 	mutex_unlock(&rdtgroup_mutex);
 	cpus_read_unlock();
 }
-- 
2.39.2