[PATCH v4 4/7] x86,fs/resctrl: Add monitor property 'mbm_cntr_assign_fixed'

Ben Horgan
2026-03-26T17:26:08Z

Commit

3b497c3f4f04 ("fs/resctrl: Introduce the interface to display monitoring modes")

introduced CONFIG_RESCTRL_ASSIGN_FIXED but left adding the Kconfig
entry until it was necessary. The counter assignment mode is fixed in
MPAM, even when there are assignable counters, and so addressing this
is needed to support MPAM.

To avoid the burden of another Kconfig entry, replace
CONFIG_RESCTRL_ASSIGN_FIXED with a new property in 'struct resctrl_mon',
'mbm_cntr_assign_fixed'.

To enable better user reporting check the new property in
resctrl_mbm_assign_mode_write().

Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since v2:
Change to a resctrl_mon property rather than a arch hook
Update the commit message to mention the property
---
fs/resctrl/monitor.c | 8 +++++++-
include/linux/resctrl.h | 2 ++
2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 8fec3dea33c3..6afa2af26ff7 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -1454,7 +1454,7 @@ int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
else
seq_puts(s, "[default]\n");

- if (!IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED)) {
+ if (!r->mon.mbm_cntr_assign_fixed) {
if (enabled)
seq_puts(s, "default\n");
else
@@ -1505,6 +1505,12 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
}

if (enable != resctrl_arch_mbm_cntr_assign_enabled(r)) {
+ if (r->mon.mbm_cntr_assign_fixed) {
+ ret = -EINVAL;
+ rdt_last_cmd_puts("Counter assignment mode is not configurable\n");
+ goto out_unlock;
+ }
+
ret = resctrl_arch_mbm_cntr_assign_set(r, enable);
if (ret)
goto out_unlock;
diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 06e8c72e8660..a986daf5f2ef 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -294,6 +294,7 @@ enum resctrl_schema_fmt {
* @mbm_assign_on_mkdir: True if counters should automatically be assigned to MBM
* events of monitor groups created via mkdir.
* @mbm_cntr_configurable: True if assignable counters are configurable.
+ * @mbm_cntr_assign_fixed: True if the counter assignment mode is fix.
*/
struct resctrl_mon {
u32 num_rmid;
@@ -302,6 +303,7 @@ struct resctrl_mon {
bool mbm_cntr_assignable;
bool mbm_assign_on_mkdir;
bool mbm_cntr_configurable;
+ bool mbm_cntr_assign_fixed;
};

/**
--
2.43.0