[PATCH v3 10/12] fs/resctrl: Expose kmode_cpus / kmode_cpus_list per rdtgroup

[Babu Moger]

rdtgrp->kmode_cpu_mask selects which CPUs of a group have the
kernel-mode binding programmed, but the mask is not visible from the
resctrl filesystem; user space has no way to verify the result of a
write to info/kernel_mode without reading kernel memory.

Add two read-only files alongside cpus / cpus_list in every rdtgroup:

  kmode_cpus       - bitmap form of rdtgrp->kmode_cpu_mask
  kmode_cpus_list  - range-list form of the same mask

The handler returns -ENOENT for a deleted group and -ENODEV for a
pseudo-locked group, mirroring rdtgroup_cpus_show().  An empty mask
reads back as a bare newline, matching the "all online CPUs" semantics
rdtgroup_config_kmode() applies to an empty kmode_cpu_mask.

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
v3: New patch to add "kmode_cpus" and "kmode_cpus_list" to support
    kernel_modes.
---
 fs/resctrl/rdtgroup.c | 53 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index faf390893109..e155160ba2b1 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -387,6 +387,44 @@ static int rdtgroup_cpus_show(struct kernfs_open_file *of,
 	return ret;
 }
 
+/*
+ * Show the per-rdtgroup kmode_cpu_mask, the set of CPUs scoped for this
+ * group's kernel-mode binding.  Backs both the "kmode_cpus" (bitmap) and
+ * "kmode_cpus_list" (range list) files; the format is selected by
+ * is_cpu_list() based on the file's RFTYPE_FLAGS_CPUS_LIST flag.
+ *
+ * An empty mask is emitted as a bare newline.  rdtgroup_config_kmode()
+ * treats an empty kmode_cpu_mask as "all online CPUs", so reading just
+ * "\n" means the binding is applied group-wide rather than restricted
+ * to a subset.
+ *
+ * Returns -ENOENT if the group has been deleted, and -ENODEV for
+ * pseudo-locked groups -- which cannot host a kernel-mode binding, so
+ * reporting an empty mask would be misleading (the empty form elsewhere
+ * means "all online CPUs").  Mirrors rdtgroup_cpus_show() for parity.
+ */
+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,
  *
@@ -2547,6 +2585,21 @@ 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