[PATCH v6 11/18] fs/resctrl: Introduce kmode_cpus/kmode_cpus_list per rdtgroup

[Babu Moger]

The RESCTRL_GLOBAL_ENABLE_PER_CPU kernel mode allows tasks to use different
allocation and monitoring associations when transitioning from user mode to
kernel mode. The mode is enabled/disabled on a per-CPU basis.

Add kmode_cpus and kmode_cpus_list to display the CPUs associated with a
kernel mode. These files are exposed only when the global_enable_per_cpu
mode is active.

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
v6: Drop rdtgrp::kmode. Rewrite changelog (not a bugfix; association).
    https://lore.kernel.org/lkml/ef8804d5-f20c-49a1-87cf-ab39437a5f0d@xxxxxxxxx/

v5: Updated the changelog.
    Removed the RDT_MODE_PSEUDO_LOCKED check and added rdtgroup->kmode check.
    Files are created hidden.

v4: Rewrote the change to be generic.

v3: New patch to add "kmode_cpus" and "kmode_cpus_list" to support
    kernel_modes.
---
 fs/resctrl/internal.h |  2 ++
 fs/resctrl/rdtgroup.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index 986b9c942fb2..6b8d14c4bd83 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -216,6 +216,7 @@ struct mongroup {
  * @mon:			mongroup related data
  * @mode:			mode of resource group
  * @mba_mbps_event:		input monitoring event id when mba_sc is enabled
+ * @kmode_cpu_mask:		CPUs in this group's kernel-mode association
  * @plr:			pseudo-locked region
  */
 struct rdtgroup {
@@ -229,6 +230,7 @@ struct rdtgroup {
 	struct mongroup			mon;
 	enum rdtgrp_mode		mode;
 	enum resctrl_event_id		mba_mbps_event;
+	struct cpumask			kmode_cpu_mask;
 	struct pseudo_lock_region	*plr;
 };
 
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 46b2cafd9411..0e638dc654c1 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -385,6 +385,31 @@ static int rdtgroup_cpus_show(struct kernfs_open_file *of,
 	return ret;
 }
 
+/*
+ * Display CPU masks for the kernel-mode associated resource group.
+ * Supports both "kmode_cpus" (bitmap format) and "kmode_cpus_list"
+ * (range list format); the output format is selected accordingly.
+ *
+ * Returns -ENOENT on error.
+ */
+static int rdtgroup_kmode_cpus_show(struct kernfs_open_file *of,
+				    struct seq_file *s, void *v)
+{
+	struct rdtgroup *rdtgrp;
+	int ret = 0;
+
+	rdtgrp = rdtgroup_kn_lock_live(of->kn);
+
+	if (!rdtgrp || rdtgrp != resctrl_kmode.rdtgrp)
+		ret = -ENOENT;
+	else
+		seq_printf(s, is_cpu_list(of) ? "%*pbl\n" : "%*pb\n",
+			   cpumask_pr_args(&rdtgrp->kmode_cpu_mask));
+	rdtgroup_kn_unlock(of->kn);
+
+	return ret;
+}
+
 /*
  * Update the PGR_ASSOC MSR on all cpus in @cpu_mask,
  *
@@ -2256,6 +2281,23 @@ static struct rftype res_common_files[] = {
 		.flags		= RFTYPE_FLAGS_CPUS_LIST,
 		.fflags		= RFTYPE_BASE,
 	},
+	{
+		.name		= "kmode_cpus",
+		.mode		= 0444,
+		.hidden		= true,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= rdtgroup_kmode_cpus_show,
+		.fflags		= RFTYPE_BASE,
+	},
+	{
+		.name		= "kmode_cpus_list",
+		.mode		= 0444,
+		.hidden		= true,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= rdtgroup_kmode_cpus_show,
+		.flags		= RFTYPE_FLAGS_CPUS_LIST,
+		.fflags		= RFTYPE_BASE,
+	},
 	{
 		.name		= "tasks",
 		.mode		= 0644,
-- 
2.43.0