[PATCH v3 06/12] fs/resctrl: Initialize the global kernel-mode policy at subsystem init

[Babu Moger <babu.moger@amd.com>]

kernel_mode feature needs to add the interface that lets user space
choose between INHERIT_CTRL_AND_MON, GLOBAL_ASSIGN_CTRL_INHERIT_MON_PER_CPU
and GLOBAL_ASSIGN_CTRL_ASSIGN_MON_PER_CPU.  Both the generic resctrl
code and the architecture layer need a single shared snapshot of the
supported and effective policy plus the resource group that backs the
global-assign modes; that snapshot is struct resctrl_kmode_cfg.

Add the file-local resctrl_kcfg and a helper resctrl_kmode_init() that:

  - Adds kmode and kmode_cur with BIT(INHERIT_CTRL_AND_MON), the
    universally supported mode and today's behaviour;
  - points k_rdtgrp at rdtgroup_default so global-assign modes have a
    valid backing group from boot;
  - calls resctrl_arch_get_kmode_support() so each architecture ORs
    BIT(<mode>) into kmode for the policies its hardware supports
    (on x86, AMD PLZA contributes the two global-assign modes).

resctrl_kmode_init() runs from resctrl_init() once the default group
has been set up.  No user-visible behaviour changes yet; later patches
expose kmode_cur via sysfs and act on changes.

Signed-off-by: Babu Moger <babu.moger@amd.com>
---
v3: Moved all the changes to resctrl FS.
    Updated changelog.
    Arch code only provides supported modes and FS decides which mode to
    be supported.

v2: New patch to handle PLZA interfaces with /sys/fs/resctrl/info/ directory.
    https://lore.kernel.org/lkml/2ab556af-095b-422b-9396-f845c6fd0342@intel.com/
---
 fs/resctrl/rdtgroup.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 5dfdaa6f9d8f..a7bfc74897cc 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 resctrl policy: hardware-supported and effective modes
+ * (see struct resctrl_kmode_cfg) and the rdtgroup backing global-assign modes.
+ * Initialized from resctrl_kmode_init() during resctrl_init().
+ */
+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
@@ -2206,6 +2213,23 @@ static void io_alloc_init(void)
 	}
 }
 
+/*
+ * Baseline the global kernel-mode resctrl configuration at boot.
+ *
+ * Initialise both the supported (kmode) and effective (kmode_cur) policy
+ * with BIT(INHERIT_CTRL_AND_MON), point k_rdtgrp at the default resource
+ * group, and let the arch hook OR in any additional modes the platform
+ * advertises (e.g. on x86, AMD PLZA adds the two global-assign modes).
+ */
+static void resctrl_kmode_init(void)
+{
+	resctrl_kcfg.kmode = BIT(INHERIT_CTRL_AND_MON);
+	resctrl_kcfg.kmode_cur = BIT(INHERIT_CTRL_AND_MON);
+	resctrl_kcfg.k_rdtgrp = &rdtgroup_default;
+
+	resctrl_arch_get_kmode_support(&resctrl_kcfg);
+}
+
 void resctrl_file_fflags_init(const char *config, unsigned long fflags)
 {
 	struct rftype *rft;
@@ -4560,6 +4584,8 @@ int resctrl_init(void)
 
 	io_alloc_init();
 
+	resctrl_kmode_init();
+
 	ret = resctrl_l3_mon_resource_init();
 	if (ret)
 		return ret;
-- 
2.43.0