[RESEND PATCH v4 09/15] fs/resctrl: Introduce kmode_cpus/kmode_cpus_list per rdtgroup

[Babu Moger]

Kernel-mode resctrl policies allow kernel work to be associated with a
specific rdtgroup, optionally restricted to a subset of online CPUs.

While user space can query the active kernel-mode policy and its associated
rdtgroup through info/kernel_mode, it currently lacks visibility into the
CPU scope of that binding.

Introduce read-only kmode_cpus and kmode_cpus_list files for each rdtgroup.
These expose rdtgrp->kmode_cpu_mask in both bitmap and range-list formats,
consistent with the existing cpus and cpus_list interfaces.

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
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 |  4 ++++
 fs/resctrl/rdtgroup.c | 46 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index 178126bb2da5..12db6933bc54 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -216,6 +216,8 @@ struct mongroup {
  * @mon:			mongroup related data
  * @mode:			mode of resource group
  * @mba_mbps_event:		input monitoring event id when mba_sc is enabled
+ * @kmode:			true if this group is bound to a kernel-mode policy
+ * @kmode_cpu_mask:		CPU scope for this group's kernel-mode binding
  * @plr:			pseudo-locked region
  */
 struct rdtgroup {
@@ -229,6 +231,8 @@ struct rdtgroup {
 	struct mongroup			mon;
 	enum rdtgrp_mode		mode;
 	enum resctrl_event_id		mba_mbps_event;
+	bool				kmode;
+	struct cpumask			kmode_cpu_mask;
 	struct pseudo_lock_region	*plr;
 };
 
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 346aa4df62a4..0d5c94169d03 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -392,6 +392,37 @@ static int rdtgroup_cpus_show(struct kernfs_open_file *of,
 	return ret;
 }
 
+/*
+ * Display per-rdtgroup CPU bindings for kernel-mode enabled groups.
+ * Supports both "kmode_cpus" (bitmap format) and "kmode_cpus_list"
+ * (range list format); the output format is selected accordingly.
+ *
+ * Returns -ENOENT if the group has been deleted, and -ENODEV for
+ * pseudo-locked groups, which cannot host a kernel-mode binding.
+ */
+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) {
+		if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
+			ret = -ENODEV;
+		} else {
+			seq_printf(s, is_cpu_list(of) ? "%*pbl\n" : "%*pb\n",
+				   cpumask_pr_args(&rdtgrp->kmode_cpu_mask));
+		}
+	} else {
+		ret = -ENOENT;
+	}
+	rdtgroup_kn_unlock(of->kn);
+
+	return ret;
+}
+
 /*
  * Update the PGR_ASSOC MSR on all cpus in @cpu_mask,
  *
@@ -2181,6 +2212,21 @@ static struct rftype res_common_files[] = {
 		.flags		= RFTYPE_FLAGS_CPUS_LIST,
 		.fflags		= RFTYPE_BASE,
 	},
+	{
+		.name		= "kmode_cpus",
+		.mode		= 0444,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= rdtgroup_kmode_cpus_show,
+		.fflags		= RFTYPE_BASE,
+	},
+	{
+		.name		= "kmode_cpus_list",
+		.mode		= 0444,
+		.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