[PATCH v2 20/29] arm_mpam: Allow configuration to be applied and restored during cpu online

James Morse
2025-09-10T20:45:11Z

When CPUs come online the MSC's original configuration should be restored.

Add struct mpam_config to hold the configuration. This has a bitmap of
features that were modified. Once the maximum partid is known, allocate
a configuration array for each component, and reprogram each RIS
configuration from this.

CC: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v1:
* Switched entry_rcu to srcu versions.

Changes since RFC:
* Added a comment about the ordering around max_partid.
* Allocate configurations after interrupts are registered to reduce churn.
* Added mpam_assert_partid_sizes_fixed();
* Make reset use an all-ones instead of zero config.
---
drivers/resctrl/mpam_devices.c | 269 +++++++++++++++++++++++++++++---
drivers/resctrl/mpam_internal.h | 29 +++-
2 files changed, 271 insertions(+), 27 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index ec1db5f8b05c..7fd149109c75 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -114,6 +114,16 @@ static LLIST_HEAD(mpam_garbage);
/* When mpam is disabled, the printed reason to aid debugging */
static char *mpam_disable_reason;

+/*
+ * Once mpam is enabled, new requestors cannot further reduce the available
+ * partid. Assert that the size is fixed, and new requestors will be turned
+ * away.
+ */
+static void mpam_assert_partid_sizes_fixed(void)
+{
+ WARN_ON_ONCE(!partid_max_published);
+}
+
static u32 __mpam_read_reg(struct mpam_msc *msc, u16 reg)
{
WARN_ON_ONCE(!cpumask_test_cpu(smp_processor_id(), &msc->accessibility));
@@ -363,12 +373,16 @@ static void mpam_class_destroy(struct mpam_class *class)
add_to_garbage(class);
}

+static void __destroy_component_cfg(struct mpam_component *comp);
+
static void mpam_comp_destroy(struct mpam_component *comp)
{
struct mpam_class *class = comp->class;

lockdep_assert_held(&mpam_list_lock);

+ __destroy_component_cfg(comp);
+
list_del_rcu(&comp->class_list);
add_to_garbage(comp);

@@ -833,50 +847,105 @@ static void mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
__mpam_write_reg(msc, reg, bm);
}

-static void mpam_reset_ris_partid(struct mpam_msc_ris *ris, u16 partid)
+/* Called via IPI. Call while holding an SRCU reference */
+static void mpam_reprogram_ris_partid(struct mpam_msc_ris *ris, u16 partid,
+ struct mpam_config *cfg)
{
struct mpam_msc *msc = ris->vmsc->msc;
struct mpam_props *rprops = &ris->props;

- mpam_assert_srcu_read_lock_held();
-
mutex_lock(&msc->part_sel_lock);
__mpam_part_sel(ris->ris_idx, partid, msc);

- if (mpam_has_feature(mpam_feat_cpor_part, rprops))
- mpam_reset_msc_bitmap(msc, MPAMCFG_CPBM, rprops->cpbm_wd);
+ if (mpam_has_feature(mpam_feat_cpor_part, rprops) &&
+ mpam_has_feature(mpam_feat_cpor_part, cfg)) {
+ if (cfg->reset_cpbm)
+ mpam_reset_msc_bitmap(msc, MPAMCFG_CPBM,
+ rprops->cpbm_wd);
+ else
+ mpam_write_partsel_reg(msc, CPBM, cfg->cpbm);
+ }

- if (mpam_has_feature(mpam_feat_mbw_part, rprops))
- mpam_reset_msc_bitmap(msc, MPAMCFG_MBW_PBM, rprops->mbw_pbm_bits);
+ if (mpam_has_feature(mpam_feat_mbw_part, rprops) &&
+ mpam_has_feature(mpam_feat_mbw_part, cfg)) {
+ if (cfg->reset_mbw_pbm)
+ mpam_reset_msc_bitmap(msc, MPAMCFG_MBW_PBM,
+ rprops->mbw_pbm_bits);
+ else
+ mpam_write_partsel_reg(msc, MBW_PBM, cfg->mbw_pbm);
+ }

- if (mpam_has_feature(mpam_feat_mbw_min, rprops))
+ if (mpam_has_feature(mpam_feat_mbw_min, rprops) &&
+ mpam_has_feature(mpam_feat_mbw_min, cfg))
mpam_write_partsel_reg(msc, MBW_MIN, 0);

- if (mpam_has_feature(mpam_feat_mbw_max, rprops))
- mpam_write_partsel_reg(msc, MBW_MAX, MPAMCFG_MBW_MAX_MAX);
+ if (mpam_has_feature(mpam_feat_mbw_max, rprops) &&
+ mpam_has_feature(mpam_feat_mbw_max, cfg))
+ mpam_write_partsel_reg(msc, MBW_MAX, cfg->mbw_max);

- if (mpam_has_feature(mpam_feat_mbw_prop, rprops))
+ if (mpam_has_feature(mpam_feat_mbw_prop, rprops) &&
+ mpam_has_feature(mpam_feat_mbw_prop, cfg))
mpam_write_partsel_reg(msc, MBW_PROP, 0);
mutex_unlock(&msc->part_sel_lock);
}

+struct reprogram_ris {
+ struct mpam_msc_ris *ris;
+ struct mpam_config *cfg;
+};
+
+/* Call with MSC lock held */
+static int mpam_reprogram_ris(void *_arg)
+{
+ u16 partid, partid_max;
+ struct reprogram_ris *arg = _arg;
+ struct mpam_msc_ris *ris = arg->ris;
+ struct mpam_config *cfg = arg->cfg;
+
+ if (ris->in_reset_state)
+ return 0;
+
+ spin_lock(&partid_max_lock);
+ partid_max = mpam_partid_max;
+ spin_unlock(&partid_max_lock);
+ for (partid = 0; partid <= partid_max; partid++)
+ mpam_reprogram_ris_partid(ris, partid, cfg);
+
+ return 0;
+}
+
+static void mpam_init_reset_cfg(struct mpam_config *reset_cfg)
+{
+ memset(reset_cfg, 0, sizeof(*reset_cfg));
+
+ reset_cfg->features = ~0;
+ reset_cfg->cpbm = ~0;
+ reset_cfg->mbw_pbm = ~0;
+ reset_cfg->mbw_max = MPAMCFG_MBW_MAX_MAX;
+
+ reset_cfg->reset_cpbm = true;
+ reset_cfg->reset_mbw_pbm = true;
+}
+
/*
* Called via smp_call_on_cpu() to prevent migration, while still being
* pre-emptible.
*/
static int mpam_reset_ris(void *arg)
{
- u16 partid, partid_max;
+ struct mpam_config reset_cfg;
struct mpam_msc_ris *ris = arg;
+ struct reprogram_ris reprogram_arg;

if (ris->in_reset_state)
return 0;

- spin_lock(&partid_max_lock);
- partid_max = mpam_partid_max;
- spin_unlock(&partid_max_lock);
- for (partid = 0; partid < partid_max; partid++)
- mpam_reset_ris_partid(ris, partid);
+ mpam_init_reset_cfg(&reset_cfg);
+
+ reprogram_arg.ris = ris;
+ reprogram_arg.cfg = &reset_cfg;
+
+ mpam_reprogram_ris(&reprogram_arg);

return 0;
}
@@ -922,6 +991,40 @@ static void mpam_reset_msc(struct mpam_msc *msc, bool online)
}
}

+static void mpam_reprogram_msc(struct mpam_msc *msc)
+{
+ u16 partid;
+ bool reset;
+ struct mpam_config *cfg;
+ struct mpam_msc_ris *ris;
+
+ /*
+ * No lock for mpam_partid_max as partid_max_published has been
+ * set by mpam_enabled(), so the values can no longer change.
+ */
+ mpam_assert_partid_sizes_fixed();
+
+ guard(srcu)(&mpam_srcu);
+ list_for_each_entry_srcu(ris, &msc->ris, msc_list,
+ srcu_read_lock_held(&mpam_srcu)) {
+ if (!mpam_is_enabled() && !ris->in_reset_state) {
+ mpam_touch_msc(msc, &mpam_reset_ris, ris);
+ ris->in_reset_state = true;
+ continue;
+ }
+
+ reset = true;
+ for (partid = 0; partid <= mpam_partid_max; partid++) {
+ cfg = &ris->vmsc->comp->cfg[partid];
+ if (cfg->features)
+ reset = false;
+
+ mpam_reprogram_ris_partid(ris, partid, cfg);
+ }
+ ris->in_reset_state = reset;
+ }
+}
+
static void _enable_percpu_irq(void *_irq)
{
int *irq = _irq;
@@ -944,7 +1047,7 @@ static int mpam_cpu_online(unsigned int cpu)
_enable_percpu_irq(&msc->reenable_error_ppi);

if (atomic_fetch_inc(&msc->online_refs) == 0)
- mpam_reset_msc(msc, true);
+ mpam_reprogram_msc(msc);
}
srcu_read_unlock(&mpam_srcu, idx);

@@ -1577,6 +1680,45 @@ static void mpam_unregister_irqs(void)
cpus_read_unlock();
}

+static void __destroy_component_cfg(struct mpam_component *comp)
+{
+ add_to_garbage(comp->cfg);
+}
+
+static int __allocate_component_cfg(struct mpam_component *comp)
+{
+ mpam_assert_partid_sizes_fixed();
+
+ if (comp->cfg)
+ return 0;
+
+ comp->cfg = kcalloc(mpam_partid_max + 1, sizeof(*comp->cfg), GFP_KERNEL);
+ if (!comp->cfg)
+ return -ENOMEM;
+ init_garbage(comp->cfg);
+
+ return 0;
+}
+
+static int mpam_allocate_config(void)
+{
+ int err = 0;
+ struct mpam_class *class;
+ struct mpam_component *comp;
+
+ lockdep_assert_held(&mpam_list_lock);
+
+ list_for_each_entry(class, &mpam_classes, classes_list) {
+ list_for_each_entry(comp, &class->components, class_list) {
+ err = __allocate_component_cfg(comp);
+ if (err)
+ return err;
+ }
+ }
+
+ return 0;
+}
+
static void mpam_enable_once(void)
{
int err;
@@ -1596,12 +1738,21 @@ static void mpam_enable_once(void)
*/
cpus_read_lock();
mutex_lock(&mpam_list_lock);
- mpam_enable_merge_features(&mpam_classes);
+ do {
+ mpam_enable_merge_features(&mpam_classes);

- err = mpam_register_irqs();
- if (err)
- pr_warn("Failed to register irqs: %d\n", err);
+ err = mpam_register_irqs();
+ if (err) {
+ pr_warn("Failed to register irqs: %d\n", err);
+ break;
+ }

+ err = mpam_allocate_config();
+ if (err) {
+ pr_err("Failed to allocate configuration arrays.\n");
+ break;
+ }
+ } while (0);
mutex_unlock(&mpam_list_lock);
cpus_read_unlock();

@@ -1624,6 +1775,9 @@ static void mpam_reset_component_locked(struct mpam_component *comp)
struct mpam_msc_ris *ris;

lockdep_assert_cpus_held();
+ mpam_assert_partid_sizes_fixed();
+
+ memset(comp->cfg, 0, (mpam_partid_max * sizeof(*comp->cfg)));

guard(srcu)(&mpam_srcu);
list_for_each_entry_srcu(vmsc, &comp->vmsc, comp_list,
@@ -1723,6 +1877,77 @@ void mpam_enable(struct work_struct *work)
mpam_enable_once();
}

+struct mpam_write_config_arg {
+ struct mpam_msc_ris *ris;
+ struct mpam_component *comp;
+ u16 partid;
+};
+
+static int __write_config(void *arg)
+{
+ struct mpam_write_config_arg *c = arg;
+
+ mpam_reprogram_ris_partid(c->ris, c->partid, &c->comp->cfg[c->partid]);
+
+ return 0;
+}
+
+#define maybe_update_config(cfg, feature, newcfg, member, changes) do { \
+ if (mpam_has_feature(feature, newcfg) && \
+ (newcfg)->member != (cfg)->member) { \
+ (cfg)->member = (newcfg)->member; \
+ cfg->features |= (1 << feature); \
+ \
+ (changes) |= (1 << feature); \
+ } \
+} while (0)
+
+static mpam_features_t mpam_update_config(struct mpam_config *cfg,
+ const struct mpam_config *newcfg)
+{
+ mpam_features_t changes = 0;
+
+ maybe_update_config(cfg, mpam_feat_cpor_part, newcfg, cpbm, changes);
+ maybe_update_config(cfg, mpam_feat_mbw_part, newcfg, mbw_pbm, changes);
+ maybe_update_config(cfg, mpam_feat_mbw_max, newcfg, mbw_max, changes);
+
+ return changes;
+}
+
+int mpam_apply_config(struct mpam_component *comp, u16 partid,
+ struct mpam_config *cfg)
+{
+ struct mpam_write_config_arg arg;
+ struct mpam_msc_ris *ris;
+ struct mpam_vmsc *vmsc;
+ struct mpam_msc *msc;
+
+ lockdep_assert_cpus_held();
+
+ /* Don't pass in the current config! */
+ WARN_ON_ONCE(&comp->cfg[partid] == cfg);
+
+ if (!mpam_update_config(&comp->cfg[partid], cfg))
+ return 0;
+
+ arg.comp = comp;
+ arg.partid = partid;
+
+ guard(srcu)(&mpam_srcu);
+ list_for_each_entry_srcu(vmsc, &comp->vmsc, comp_list,
+ srcu_read_lock_held(&mpam_srcu)) {
+ msc = vmsc->msc;
+
+ list_for_each_entry_srcu(ris, &vmsc->ris, vmsc_list,
+ srcu_read_lock_held(&mpam_srcu)) {
+ arg.ris = ris;
+ mpam_touch_msc(msc, __write_config, &arg);
+ }
+ }
+
+ return 0;
+}
+
static int __init mpam_msc_driver_init(void)
{
if (!system_supports_mpam())
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index b69fa9199cb4..17570d9aae9b 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -169,11 +169,7 @@ struct mpam_props {
u16 num_mbwu_mon;
};

-static inline bool mpam_has_feature(enum mpam_device_features feat,
- struct mpam_props *props)
-{
- return (1 << feat) & props->features;
-}
+#define mpam_has_feature(_feat, x) ((1 << (_feat)) & (x)->features)

static inline void mpam_set_feature(enum mpam_device_features feat,
struct mpam_props *props)
@@ -204,6 +200,20 @@ struct mpam_class {
struct mpam_garbage garbage;
};

+struct mpam_config {
+ /* Which configuration values are valid. */
+ mpam_features_t features;
+
+ u32 cpbm;
+ u32 mbw_pbm;
+ u16 mbw_max;
+
+ bool reset_cpbm;
+ bool reset_mbw_pbm;
+
+ struct mpam_garbage garbage;
+};
+
struct mpam_component {
u32 comp_id;

@@ -212,6 +222,12 @@ struct mpam_component {

cpumask_t affinity;

+ /*
+ * Array of configuration values, indexed by partid.
+ * Read from cpuhp callbacks, hold the cpuhp lock when writing.
+ */
+ struct mpam_config *cfg;
+
/* member of mpam_class:components */
struct list_head class_list;

@@ -276,6 +292,9 @@ extern u8 mpam_pmg_max;
void mpam_enable(struct work_struct *work);
void mpam_disable(struct work_struct *work);

+int mpam_apply_config(struct mpam_component *comp, u16 partid,
+ struct mpam_config *cfg);
+
int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
cpumask_t *affinity);

--
2.39.5