[PATCH v4 13/41] arm_mpam: resctrl: Add boilerplate cpuhp and domain allocation

Ben Horgan
2026-02-03T21:45:16Z

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

resctrl has its own data structures to describe its resources. We can't use
these directly as we play tricks with the 'MBA' resource, picking the MPAM
controls or monitors that best apply. We may export the same component as
both L3 and MBA.

Add mpam_resctrl_exports[] as the array of class->resctrl mappings we are
exporting, and add the cpuhp hooks that allocated and free the resctrl
domain structures.

While we're here, plumb in a few other obvious things.

CONFIG_ARM_CPU_RESCTRL is used to allow this code to be built even though
it can't yet be linked against resctrl.

Tested-by: Gavin Shan <gshan@redhat.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since rfc:
Domain list is an rcu list
Add synchronize_rcu() to free the deleted element
Code flow simplification (Jonathan)

Changes since v2:
Iterate over mpam_resctrl_dom directly (Jonathan)
Code flow clarification
Comment tidying
Remove power of 2 check as no longer creates holes in rmid indices
Remove unused type argument
add macro helper for_each_mpam_resctrl_control

Changes since v3:
Add and use mpam_resctrl_online_domain_hdr()
mpam_resctrl_alloc_domain() error paths (Reinette)
rebase on x86/cache changes rdt_mon_domain becomes rdt_l3_mon_domain etc
---
drivers/resctrl/Makefile | 1 +
drivers/resctrl/mpam_devices.c | 12 ++
drivers/resctrl/mpam_internal.h | 23 ++-
drivers/resctrl/mpam_resctrl.c | 343 ++++++++++++++++++++++++++++++++
include/linux/arm_mpam.h | 3 +
5 files changed, 381 insertions(+), 1 deletion(-)
create mode 100644 drivers/resctrl/mpam_resctrl.c

diff --git a/drivers/resctrl/Makefile b/drivers/resctrl/Makefile
index 898199dcf80d..40beaf999582 100644
--- a/drivers/resctrl/Makefile
+++ b/drivers/resctrl/Makefile
@@ -1,4 +1,5 @@
obj-$(CONFIG_ARM64_MPAM_DRIVER) += mpam.o
mpam-y += mpam_devices.o
+mpam-$(CONFIG_ARM_CPU_RESCTRL) += mpam_resctrl.o

ccflags-$(CONFIG_ARM64_MPAM_DRIVER_DEBUG) += -DDEBUG
diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 860181266b15..b81d5c7f44ca 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -1628,6 +1628,9 @@ static int mpam_cpu_online(unsigned int cpu)
mpam_reprogram_msc(msc);
}

+ if (mpam_is_enabled())
+ return mpam_resctrl_online_cpu(cpu);
+
return 0;
}

@@ -1671,6 +1674,9 @@ static int mpam_cpu_offline(unsigned int cpu)
{
struct mpam_msc *msc;

+ if (mpam_is_enabled())
+ mpam_resctrl_offline_cpu(cpu);
+
guard(srcu)(&mpam_srcu);
list_for_each_entry_srcu(msc, &mpam_all_msc, all_msc_list,
srcu_read_lock_held(&mpam_srcu)) {
@@ -2517,6 +2523,12 @@ static void mpam_enable_once(void)
mutex_unlock(&mpam_list_lock);
cpus_read_unlock();

+ if (!err) {
+ err = mpam_resctrl_setup();
+ if (err)
+ pr_err("Failed to initialise resctrl: %d\n", err);
+ }
+
if (err) {
mpam_disable_reason = "Failed to enable.";
schedule_work(&mpam_broken_work);
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index 8983dbe715c2..a9d89d9e18a8 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -12,7 +12,7 @@
#include <linux/jump_label.h>
#include <linux/llist.h>
#include <linux/mutex.h>
-#include <linux/srcu.h>
+#include <linux/resctrl.h>
#include <linux/spinlock.h>
#include <linux/srcu.h>
#include <linux/types.h>
@@ -334,6 +334,17 @@ struct mpam_msc_ris {
struct mpam_garbage garbage;
};

+struct mpam_resctrl_dom {
+ struct mpam_component *ctrl_comp;
+ struct rdt_ctrl_domain resctrl_ctrl_dom;
+ struct rdt_l3_mon_domain resctrl_mon_dom;
+};
+
+struct mpam_resctrl_res {
+ struct mpam_class *class;
+ struct rdt_resource resctrl_res;
+};
+
static inline int mpam_alloc_csu_mon(struct mpam_class *class)
{
struct mpam_props *cprops = &class->props;
@@ -388,6 +399,16 @@ void mpam_msmon_reset_mbwu(struct mpam_component *comp, struct mon_cfg *ctx);
int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
cpumask_t *affinity);

+#ifdef CONFIG_RESCTRL_FS
+int mpam_resctrl_setup(void);
+int mpam_resctrl_online_cpu(unsigned int cpu);
+void mpam_resctrl_offline_cpu(unsigned int cpu);
+#else
+static inline int mpam_resctrl_setup(void) { return 0; }
+static inline int mpam_resctrl_online_cpu(unsigned int cpu) { return 0; }
+static inline void mpam_resctrl_offline_cpu(unsigned int cpu) { }
+#endif /* CONFIG_RESCTRL_FS */
+
/*
* MPAM MSCs have the following register layout. See:
* Arm Memory System Resource Partitioning and Monitoring (MPAM) System
diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
new file mode 100644
index 000000000000..4c2248c92955
--- /dev/null
+++ b/drivers/resctrl/mpam_resctrl.c
@@ -0,0 +1,343 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2025 Arm Ltd.
+
+#define pr_fmt(fmt) "%s:%s: " fmt, KBUILD_MODNAME, __func__
+
+#include <linux/arm_mpam.h>
+#include <linux/cacheinfo.h>
+#include <linux/cpu.h>
+#include <linux/cpumask.h>
+#include <linux/errno.h>
+#include <linux/list.h>
+#include <linux/printk.h>
+#include <linux/rculist.h>
+#include <linux/resctrl.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+
+#include <asm/mpam.h>
+
+#include "mpam_internal.h"
+
+/*
+ * The classes we've picked to map to resctrl resources, wrapped
+ * in with their resctrl structure.
+ * Class pointer may be NULL.
+ */
+static struct mpam_resctrl_res mpam_resctrl_controls[RDT_NUM_RESOURCES];
+
+#define for_each_mpam_resctrl_control(res, rid) \
+ for (rid = 0, res = &mpam_resctrl_controls[rid]; \
+ rid < RDT_NUM_RESOURCES; \
+ rid++, res = &mpam_resctrl_controls[rid])
+
+/* The lock for modifying resctrl's domain lists from cpuhp callbacks. */
+static DEFINE_MUTEX(domain_list_lock);
+
+static bool exposed_alloc_capable;
+static bool exposed_mon_capable;
+
+bool resctrl_arch_alloc_capable(void)
+{
+ return exposed_alloc_capable;
+}
+
+bool resctrl_arch_mon_capable(void)
+{
+ return exposed_mon_capable;
+}
+
+/*
+ * MSC may raise an error interrupt if it sees an out or range partid/pmg,
+ * and go on to truncate the value. Regardless of what the hardware supports,
+ * only the system wide safe value is safe to use.
+ */
+u32 resctrl_arch_get_num_closid(struct rdt_resource *ignored)
+{
+ return mpam_partid_max + 1;
+}
+
+struct rdt_resource *resctrl_arch_get_resource(enum resctrl_res_level l)
+{
+ if (l >= RDT_NUM_RESOURCES)
+ return NULL;
+
+ return &mpam_resctrl_controls[l].resctrl_res;
+}
+
+static int mpam_resctrl_control_init(struct mpam_resctrl_res *res)
+{
+ /* TODO: initialise the resctrl resources */
+
+ return 0;
+}
+
+static int mpam_resctrl_pick_domain_id(int cpu, struct mpam_component *comp)
+{
+ struct mpam_class *class = comp->class;
+
+ if (class->type == MPAM_CLASS_CACHE)
+ return comp->comp_id;
+
+ /* TODO: repaint domain ids to match the L3 domain ids */
+ /* Otherwise, expose the ID used by the firmware table code. */
+ return comp->comp_id;
+}
+
+static void mpam_resctrl_domain_hdr_init(int cpu, struct mpam_component *comp,
+ struct rdt_domain_hdr *hdr)
+{
+ lockdep_assert_cpus_held();
+
+ INIT_LIST_HEAD(&hdr->list);
+ hdr->id = mpam_resctrl_pick_domain_id(cpu, comp);
+ cpumask_set_cpu(cpu, &hdr->cpu_mask);
+}
+
+static void mpam_resctrl_online_domain_hdr(unsigned int cpu,
+ struct rdt_domain_hdr *hdr)
+{
+ lockdep_assert_cpus_held();
+
+ cpumask_set_cpu(cpu, &hdr->cpu_mask);
+}
+
+/**
+ * mpam_resctrl_offline_domain_hdr() - Update the domain header to remove a CPU.
+ * @cpu: The CPU to remove from the domain.
+ * @hdr: The domain's header.
+ *
+ * Removes @cpu from the header mask. If this was the last CPU in the domain,
+ * the domain header is removed from its parent list and true is returned,
+ * indicating the parent structure can be freed.
+ * If there are other CPUs in the domain, returns false.
+ */
+static bool mpam_resctrl_offline_domain_hdr(unsigned int cpu,
+ struct rdt_domain_hdr *hdr)
+{
+ lockdep_assert_held(&domain_list_lock);
+
+ cpumask_clear_cpu(cpu, &hdr->cpu_mask);
+ if (cpumask_empty(&hdr->cpu_mask)) {
+ list_del_rcu(&hdr->list);
+ synchronize_rcu();
+ return true;
+ }
+
+ return false;
+}
+
+static struct mpam_resctrl_dom *
+mpam_resctrl_alloc_domain(unsigned int cpu, struct mpam_resctrl_res *res)
+{
+ int err;
+ struct mpam_resctrl_dom *dom;
+ struct rdt_l3_mon_domain *mon_d;
+ struct rdt_ctrl_domain *ctrl_d;
+ struct mpam_class *class = res->class;
+ struct mpam_component *comp_iter, *ctrl_comp;
+ struct rdt_resource *r = &res->resctrl_res;
+
+ lockdep_assert_held(&domain_list_lock);
+
+ ctrl_comp = NULL;
+ guard(srcu)(&mpam_srcu);
+ list_for_each_entry_srcu(comp_iter, &class->components, class_list,
+ srcu_read_lock_held(&mpam_srcu)) {
+ if (cpumask_test_cpu(cpu, &comp_iter->affinity)) {
+ ctrl_comp = comp_iter;
+ break;
+ }
+ }
+
+ /* class has no component for this CPU */
+ if (WARN_ON_ONCE(!ctrl_comp))
+ return ERR_PTR(-EINVAL);
+
+ dom = kzalloc_node(sizeof(*dom), GFP_KERNEL, cpu_to_node(cpu));
+ if (!dom)
+ return ERR_PTR(-ENOMEM);
+
+ if (exposed_alloc_capable) {
+ dom->ctrl_comp = ctrl_comp;
+
+ ctrl_d = &dom->resctrl_ctrl_dom;
+ mpam_resctrl_domain_hdr_init(cpu, ctrl_comp, &ctrl_d->hdr);
+ ctrl_d->hdr.type = RESCTRL_CTRL_DOMAIN;
+ err = resctrl_online_ctrl_domain(r, ctrl_d);
+ if (err)
+ goto free_domain;
+
+ /* TODO: this list should be sorted */
+ list_add_tail_rcu(&ctrl_d->hdr.list, &r->ctrl_domains);
+ } else {
+ pr_debug("Skipped control domain online - no controls\n");
+ }
+
+ if (exposed_mon_capable) {
+ mon_d = &dom->resctrl_mon_dom;
+ mpam_resctrl_domain_hdr_init(cpu, any_mon_comp, &mon_d->hdr);
+ mon_d->hdr.type = RESCTRL_MON_DOMAIN;
+ err = resctrl_online_mon_domain(r, &mon_d->hdr);
+ if (err)
+ goto offline_ctrl_domain;
+
+ /* TODO: this list should be sorted */
+ list_add_tail_rcu(&mon_d->hdr.list, &r->mon_domains);
+ } else {
+ pr_debug("Skipped monitor domain online - no monitors\n");
+ }
+
+ return dom;
+
+offline_ctrl_domain:
+ if (exposed_alloc_capable) {
+ mpam_resctrl_offline_domain_hdr(cpu, &ctrl_d->hdr);
+ resctrl_offline_ctrl_domain(r, ctrl_d);
+ }
+free_domain:
+ kfree(dom);
+ dom = ERR_PTR(err);
+
+ return dom;
+}
+
+static struct mpam_resctrl_dom *
+mpam_resctrl_get_domain_from_cpu(int cpu, struct mpam_resctrl_res *res)
+{
+ struct mpam_resctrl_dom *dom;
+ struct rdt_resource *r = &res->resctrl_res;
+
+ lockdep_assert_cpus_held();
+
+ list_for_each_entry_rcu(dom, &r->ctrl_domains, resctrl_ctrl_dom.hdr.list) {
+ if (cpumask_test_cpu(cpu, &dom->ctrl_comp->affinity))
+ return dom;
+ }
+
+ return NULL;
+}
+
+int mpam_resctrl_online_cpu(unsigned int cpu)
+{
+ struct mpam_resctrl_res *res;
+ enum resctrl_res_level rid;
+
+ guard(mutex)(&domain_list_lock);
+ for_each_mpam_resctrl_control(res, rid) {
+ struct mpam_resctrl_dom *dom;
+
+ if (!res->class)
+ continue; // dummy_resource;
+
+ dom = mpam_resctrl_get_domain_from_cpu(cpu, res);
+ if (!dom) {
+ dom = mpam_resctrl_alloc_domain(cpu, res);
+ } else {
+ if (exposed_alloc_capable) {
+ struct rdt_ctrl_domain *ctrl_d = &dom->resctrl_ctrl_dom;
+
+ mpam_resctrl_online_domain_hdr(cpu, &ctrl_d->hdr);
+ }
+ if (exposed_mon_capable) {
+ struct rdt_l3_mon_domain *mon_d = &dom->resctrl_mon_dom;
+
+ mpam_resctrl_online_domain_hdr(cpu, &mon_d->hdr);
+ }
+ }
+ if (IS_ERR(dom))
+ return PTR_ERR(dom);
+ }
+
+ resctrl_online_cpu(cpu);
+
+ return 0;
+}
+
+void mpam_resctrl_offline_cpu(unsigned int cpu)
+{
+ struct mpam_resctrl_res *res;
+ enum resctrl_res_level rid;
+
+ resctrl_offline_cpu(cpu);
+
+ guard(mutex)(&domain_list_lock);
+ for_each_mpam_resctrl_control(res, rid) {
+ struct mpam_resctrl_dom *dom;
+ struct rdt_l3_mon_domain *mon_d;
+ struct rdt_ctrl_domain *ctrl_d;
+ bool ctrl_dom_empty, mon_dom_empty;
+
+ if (!res->class)
+ continue; // dummy resource
+
+ dom = mpam_resctrl_get_domain_from_cpu(cpu, res);
+ if (WARN_ON_ONCE(!dom))
+ continue;
+
+ if (exposed_alloc_capable) {
+ ctrl_d = &dom->resctrl_ctrl_dom;
+ ctrl_dom_empty = mpam_resctrl_offline_domain_hdr(cpu, &ctrl_d->hdr);
+ if (ctrl_dom_empty)
+ resctrl_offline_ctrl_domain(&res->resctrl_res, ctrl_d);
+ } else {
+ ctrl_dom_empty = true;
+ }
+
+ if (exposed_mon_capable) {
+ mon_d = &dom->resctrl_mon_dom;
+ mon_dom_empty = mpam_resctrl_offline_domain_hdr(cpu, &mon_d->hdr);
+ if (mon_dom_empty)
+ resctrl_offline_mon_domain(&res->resctrl_res, &mon_d->hdr);
+ } else {
+ mon_dom_empty = true;
+ }
+
+ if (ctrl_dom_empty && mon_dom_empty)
+ kfree(dom);
+ }
+}
+
+int mpam_resctrl_setup(void)
+{
+ int err = 0;
+ struct mpam_resctrl_res *res;
+ enum resctrl_res_level rid;
+
+ cpus_read_lock();
+ for_each_mpam_resctrl_control(res, rid) {
+ INIT_LIST_HEAD_RCU(&res->resctrl_res.ctrl_domains);
+ INIT_LIST_HEAD_RCU(&res->resctrl_res.mon_domains);
+ res->resctrl_res.rid = rid;
+ }
+
+ /* TODO: pick MPAM classes to map to resctrl resources */
+
+ /* Initialise the resctrl structures from the classes */
+ for_each_mpam_resctrl_control(res, rid) {
+ if (!res->class)
+ continue; // dummy resource
+
+ err = mpam_resctrl_control_init(res);
+ if (err) {
+ pr_debug("Failed to initialise rid %u\n", rid);
+ break;
+ }
+ }
+ cpus_read_unlock();
+
+ if (err) {
+ pr_debug("Internal error %d - resctrl not supported\n", err);
+ return err;
+ }
+
+ if (!exposed_alloc_capable && !exposed_mon_capable) {
+ pr_debug("No alloc(%u) or monitor(%u) found - resctrl not supported\n",
+ exposed_alloc_capable, exposed_mon_capable);
+ return -EOPNOTSUPP;
+ }
+
+ /* TODO: call resctrl_init() */
+
+ return 0;
+}
diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
index 7f00c5285a32..2c7d1413a401 100644
--- a/include/linux/arm_mpam.h
+++ b/include/linux/arm_mpam.h
@@ -49,6 +49,9 @@ static inline int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
}
#endif

+bool resctrl_arch_alloc_capable(void);
+bool resctrl_arch_mon_capable(void);
+
/**
* mpam_register_requestor() - Register a requestor with the MPAM driver
* @partid_max: The maximum PARTID value the requestor can generate.
--
2.43.0