[PATCH 23/33] arm_mpam: Allow configuration to be applied and restored during cpu online

Ben Horgan
2025-11-07T12:37:28Z

From: James Morse <james.morse@arm.com>

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>
Cc: Shaopeng Tan (Fujitsu) tan.shaopeng@fujitsu.com
Cc: Peter Newman peternewman@google.com
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since v3:
Drop tags
Fix component reset, otherwise cpbm wrong and controls not set.
Add a cfg_lock to guard configuration of an msc
---
drivers/resctrl/mpam_devices.c | 268 ++++++++++++++++++++++++++++++--
drivers/resctrl/mpam_internal.h | 27 ++++
2 files changed, 280 insertions(+), 15 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 3a0ad8d93fff..8b0944bdaf28 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -144,6 +144,16 @@ static void mpam_free_garbage(void)
}
}

+/*
+ * 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));
@@ -343,6 +353,7 @@ mpam_component_alloc(struct mpam_class *class, int id)
return comp;
}

+static void __destroy_component_cfg(struct mpam_component *comp);
static void mpam_class_destroy(struct mpam_class *class);

static void mpam_component_destroy(struct mpam_component *comp)
@@ -351,6 +362,8 @@ static void mpam_component_destroy(struct mpam_component *comp)

lockdep_assert_held(&mpam_list_lock);

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

@@ -820,31 +833,59 @@ 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;

- WARN_ON_ONCE(!srcu_read_lock_held((&mpam_srcu)));
-
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)) {
+ if (cfg->reset_mbw_max)
+ mpam_write_partsel_reg(msc, MBW_MAX, MPAMCFG_MBW_MAX_MAX);
+ else
+ mpam_write_partsel_reg(msc, MBW_MAX, cfg->mbw_max);
+ }

mutex_unlock(&msc->part_sel_lock);
}

+static void mpam_init_reset_cfg(struct mpam_config *reset_cfg)
+{
+ *reset_cfg = (struct mpam_config) {
+ .reset_cpbm = true,
+ .reset_mbw_pbm = true,
+ .reset_mbw_max = true,
+ };
+ bitmap_fill(reset_cfg->features, MPAM_FEATURE_LAST);
+}
+
/*
* Called via smp_call_on_cpu() to prevent migration, while still being
* pre-emptible. Caller must hold mpam_srcu.
@@ -852,16 +893,19 @@ static void mpam_reset_ris_partid(struct mpam_msc_ris *ris, u16 partid)
static int mpam_reset_ris(void *arg)
{
u16 partid, partid_max;
+ struct mpam_config reset_cfg;
struct mpam_msc_ris *ris = arg;

if (ris->in_reset_state)
return 0;

+ mpam_init_reset_cfg(&reset_cfg);
+
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_reprogram_ris_partid(ris, partid, &reset_cfg);

return 0;
}
@@ -894,6 +938,7 @@ static void mpam_reset_msc(struct mpam_msc *msc, bool online)
{
struct mpam_msc_ris *ris;

+ mutex_lock(&msc->cfg_lock);
list_for_each_entry_srcu(ris, &msc->ris, msc_list, srcu_read_lock_held(&mpam_srcu)) {
mpam_touch_msc(msc, &mpam_reset_ris, ris);

@@ -903,6 +948,61 @@ static void mpam_reset_msc(struct mpam_msc *msc, bool online)
*/
ris->in_reset_state = online;
}
+ mutex_unlock(&msc->cfg_lock);
+}
+
+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;
+}
+
+static void mpam_reprogram_msc(struct mpam_msc *msc)
+{
+ u16 partid;
+ bool reset;
+ struct mpam_config *cfg;
+ struct mpam_msc_ris *ris;
+ struct mpam_write_config_arg arg;
+
+ /*
+ * 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();
+
+ mutex_lock(&msc->cfg_lock);
+ 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;
+ }
+
+ arg.comp = ris->vmsc->comp;
+ arg.ris = ris;
+ reset = true;
+ for (partid = 0; partid <= mpam_partid_max; partid++) {
+ cfg = &ris->vmsc->comp->cfg[partid];
+ if (!bitmap_empty(cfg->features, MPAM_FEATURE_LAST))
+ reset = false;
+
+ arg.partid = partid;
+ mpam_touch_msc(msc, __write_config, &arg);
+ }
+ ris->in_reset_state = reset;
+ }
+ mutex_unlock(&msc->cfg_lock);
}

static void _enable_percpu_irq(void *_irq)
@@ -926,7 +1026,7 @@ 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);
}

return 0;
@@ -1125,6 +1225,9 @@ static struct mpam_msc *do_mpam_msc_drv_probe(struct platform_device *pdev)
if (err)
return ERR_PTR(err);
err = devm_mutex_init(dev, &msc->error_irq_lock);
+ if (err)
+ return ERR_PTR(err);
+ err = devm_mutex_init(dev, &msc->cfg_lock);
if (err)
return ERR_PTR(err);
mpam_mon_sel_lock_init(msc);
@@ -1585,6 +1688,70 @@ static void mpam_unregister_irqs(void)
}
}

+static void __destroy_component_cfg(struct mpam_component *comp)
+{
+ add_to_garbage(comp->cfg);
+}
+
+static void mpam_reset_component_cfg(struct mpam_component *comp)
+{
+ int i;
+ struct mpam_props *cprops = &comp->class->props;
+
+ mpam_assert_partid_sizes_fixed();
+
+ if (!comp->cfg)
+ return;
+
+ for (i = 0; i <= mpam_partid_max; i++) {
+ comp->cfg[i] = (struct mpam_config) {};
+ bitmap_fill(comp->cfg[i].features, MPAM_FEATURE_LAST);
+ bitmap_set((unsigned long *)&comp->cfg[i].cpbm, 0, cprops->cpbm_wd);
+ bitmap_set((unsigned long *)&comp->cfg[i].mbw_pbm, 0, cprops->mbw_pbm_bits);
+ bitmap_set((unsigned long *)&comp->cfg[i].mbw_max, 16 - cprops->bwa_wd, cprops->bwa_wd);
+ }
+}
+
+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;
+
+ /*
+ * The array is free()d in one go, so only cfg[0]'s structure needs
+ * to be initialised.
+ */
+ init_garbage(&comp->cfg[0].garbage);
+
+ mpam_reset_component_cfg(comp);
+
+ return 0;
+}
+
+static int mpam_allocate_config(void)
+{
+ 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) {
+ int err = __allocate_component_cfg(comp);
+ if (err)
+ return err;
+ }
+ }
+
+ return 0;
+}
+
static void mpam_enable_once(void)
{
int err;
@@ -1604,15 +1771,25 @@ 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();
+ 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();

if (err) {
- pr_warn("Failed to register irqs: %d\n", err);
mpam_disable_reason = "Failed to enable.";
schedule_work(&mpam_broken_work);
return;
@@ -1632,6 +1809,9 @@ static void mpam_reset_component_locked(struct mpam_component *comp)
struct mpam_vmsc *vmsc;

lockdep_assert_cpus_held();
+ mpam_assert_partid_sizes_fixed();
+
+ mpam_reset_component_cfg(comp);

guard(srcu)(&mpam_srcu);
list_for_each_entry_srcu(vmsc, &comp->vmsc, comp_list,
@@ -1732,6 +1912,64 @@ void mpam_enable(struct work_struct *work)
mpam_enable_once();
}

+#define maybe_update_config(cfg, feature, newcfg, member, changes) do { \
+ if (mpam_has_feature(feature, newcfg) && \
+ (newcfg)->member != (cfg)->member) { \
+ (cfg)->member = (newcfg)->member; \
+ mpam_set_feature(feature, cfg); \
+ \
+ (changes) = true; \
+ } \
+} while (0)
+
+static bool mpam_update_config(struct mpam_config *cfg,
+ const struct mpam_config *newcfg)
+{
+ bool has_changes = false;
+
+ maybe_update_config(cfg, mpam_feat_cpor_part, newcfg, cpbm, has_changes);
+ maybe_update_config(cfg, mpam_feat_mbw_part, newcfg, mbw_pbm, has_changes);
+ maybe_update_config(cfg, mpam_feat_mbw_max, newcfg, mbw_max, has_changes);
+
+ return has_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;
+
+ mutex_lock(&msc->cfg_lock);
+ 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);
+ }
+ mutex_unlock(&msc->cfg_lock);
+ }
+
+ 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 c6937161877a..842d32f148b5 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -91,6 +91,9 @@ struct mpam_msc {
*/
struct mutex part_sel_lock;

+ /* cfg_lock protects the msc configuration. */
+ struct mutex cfg_lock;
+
/*
* mon_sel_lock protects access to the MSC hardware registers that are
* affected by MPAMCFG_MON_SEL, and the mbwu_state.
@@ -180,6 +183,21 @@ struct mpam_class {
struct mpam_garbage garbage;
};

+struct mpam_config {
+ /* Which configuration values are valid. */
+ DECLARE_BITMAP(features, MPAM_FEATURE_LAST);
+
+ u32 cpbm;
+ u32 mbw_pbm;
+ u16 mbw_max;
+
+ bool reset_cpbm;
+ bool reset_mbw_pbm;
+ bool reset_mbw_max;
+
+ struct mpam_garbage garbage;
+};
+
struct mpam_component {
u32 comp_id;

@@ -188,6 +206,12 @@ 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;

@@ -247,6 +271,9 @@ 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);

--
2.43.0