[PATCH v5 06/16] fs/resctrl: Introduce kernel mode states for resctrl

[Babu Moger]

Architectures need the generic resctrl filesystem to track supported
kernel modes, the active mode, and per-dimension assignment state.

Generic resctrl has no place to store this policy state today.

Add struct resctrl_kmode_cfg to hold supported modes, active mode,
control/monitoring assignment state, and the bound resource group.
Initialize defaults from resctrl_arch_alloc_capable() and
resctrl_arch_mon_capable() during resctrl_init().

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
v5: Replace per-mode registration helpers with a single resctrl_kmode_cfg
    structure. Derive ctrl_en and mon_en from resctrl_arch_alloc_capable()
    and resctrl_arch_mon_capable() during filesystem init. Update code
    comments and changelog.

v4: New patch to initialize supported kernel modes.
    https://lore.kernel.org/lkml/737a4228-52fb-4583-ac64-8efe79c107e6@xxxxxxxxx/
    Changed the kmode_cur to enum resctrl_kernel_mode in resctrl_kmode_cfg.
    Moved the resctrl_kmode_cfg to filesystem code.
---
 fs/resctrl/internal.h | 51 +++++++++++++++++++++++++++++++++++++++++++
 fs/resctrl/rdtgroup.c | 33 ++++++++++++++++++++++++++++
 2 files changed, 84 insertions(+)

diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index e62a277dee85..4087bf44a06d 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -314,6 +314,57 @@ struct mbm_state {
 	u32	prev_bw;
 };
 
+/**
+ * enum kmode_state - Control or monitoring state for a kernel mode
+ * @KMODE_INHERIT: Inherit from the user space task.
+ * @KMODE_ASSIGN: Use a global assignment for kernel mode.
+ */
+enum kmode_state {
+	KMODE_INHERIT,
+	KMODE_ASSIGN
+};
+
+/**
+ * struct resctrl_kmode_caps - Static kernel mode capabilities
+ * @kmode_sup:	Bitmap of supported kernel modes. Empty when neither
+ *		@ctrl_en nor @mon_en is set and kernel mode policy is
+ *		unavailable on this system.
+ * @ctrl_en:	Whether kernel mode may use global assignment for control.
+ * @mon_en:	Whether kernel mode may use global assignment for monitoring.
+ */
+struct resctrl_kmode_caps {
+	DECLARE_BITMAP(kmode_sup, RESCTRL_NUM_KERNEL_MODES);
+	bool				ctrl_en;
+	bool				mon_en;
+};
+
+/**
+ * struct resctrl_kmode_active - Runtime kernel mode state
+ * @kmode_cur:	Currently selected kernel mode.
+ * @ctrl_mode:	Control assignment state when kernel mode is active.
+ * @mon_mode:	Monitoring assignment state when kernel mode is active.
+ * @k_rdtgrp:	Resource group backing global assignment mode.
+ *
+ * When @kmode_cur is %RESCTRL_INHERIT_USER, assignment state is ignored and
+ * @k_rdtgrp is %NULL.
+ */
+struct resctrl_kmode_active {
+	enum resctrl_kernel_mode	kmode_cur;
+	enum kmode_state		ctrl_mode;
+	enum kmode_state		mon_mode;
+	struct rdtgroup			*k_rdtgrp;
+};
+
+/**
+ * struct resctrl_kmode_cfg - Global kernel mode state
+ * @caps:	Supported modes and assignment capabilities.
+ * @active:	Active mode, assignment state, and assigned group.
+ */
+struct resctrl_kmode_cfg {
+	struct resctrl_kmode_caps	caps;
+	struct resctrl_kmode_active	active;
+};
+
 extern struct mutex rdtgroup_mutex;
 
 static inline const char *rdt_kn_name(const struct kernfs_node *kn)
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 5dcbb0a964e8..3c53f3f74e5a 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -76,6 +76,13 @@ static void rdtgroup_destroy_root(void);
 
 struct dentry *debugfs_resctrl;
 
+/*
+ * Global kernel mode policy state: supported modes, active mode, assignment
+ * capabilities, assignment state, and the resource group selected for a global
+ * assignment.
+ */
+static struct resctrl_kmode_cfg resctrl_kcfg;
+
 /*
  * Memory bandwidth monitoring event to use for the default CTRL_MON group
  * and each new CTRL_MON group created by the user.  Only relevant when
@@ -2297,6 +2304,30 @@ static void io_alloc_init(void)
 	}
 }
 
+/*
+ * Initialize kernel mode policy defaults from architecture capabilities.
+ *
+ * When ctrl_en or mon_en is set, RESCTRL_INHERIT_USER is supported and
+ * selected as the initial active mode. When neither is set, kmode_sup is
+ * left empty, kernel mode policy is unavailable, and kmode_cur remains at
+ * its zero-initialized default (RESCTRL_INHERIT_USER) but is unused.
+ */
+static void resctrl_kmode_init(void)
+{
+	resctrl_kcfg.caps.ctrl_en = resctrl_arch_alloc_capable();
+	resctrl_kcfg.active.ctrl_mode = KMODE_INHERIT;
+	resctrl_kcfg.caps.mon_en = resctrl_arch_mon_capable();
+	resctrl_kcfg.active.mon_mode = KMODE_INHERIT;
+	resctrl_kcfg.active.k_rdtgrp = NULL;
+
+	if (resctrl_kcfg.caps.ctrl_en || resctrl_kcfg.caps.mon_en) {
+		resctrl_kcfg.active.kmode_cur = RESCTRL_INHERIT_USER;
+		__set_bit(RESCTRL_INHERIT_USER, resctrl_kcfg.caps.kmode_sup);
+	} else {
+		bitmap_zero(resctrl_kcfg.caps.kmode_sup, RESCTRL_NUM_KERNEL_MODES);
+	}
+}
+
 void resctrl_file_fflags_init(const char *config, unsigned long fflags)
 {
 	struct rftype *rft;
@@ -4816,6 +4847,8 @@ int resctrl_init(void)
 	if (ret)
 		return ret;
 
+	resctrl_kmode_init();
+
 	ret = sysfs_create_mount_point(fs_kobj, "resctrl");
 	if (ret) {
 		resctrl_l3_mon_resource_exit();
-- 
2.43.0