Re: [PATCH v5 13/41] arm_mpam: resctrl: Add boilerplate cpuhp and domain allocation

Gavin Shan
2026-03-10T06:17:31Z

Hi Ben,

On 2/25/26 3:56 AM, Ben Horgan wrote:
> 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_res[] as the array of class->resctrl mappings we are
> exporting, and add the cpuhp hooks that allocated and free the resctrl
> domain structures. Only the mpam control feature are considered here and
> monitor support will be added later.
>
> 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.
>

CONFIG_ARM_CPU_RESCTRL isn't valid. I guess you're probably mentioning
CONFIG_ARCH_HAS_CPU_RESCTRL?

> Tested-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
> Tested-by: Peter Newman <peternewman@google.com>
> Tested-by: Zeng Heng <zengheng4@huawei.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.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
>
> Changes since v4:
> Set rid in domain_hdr
> Use rescctrl_res.alloc_capable to determine if alloc_capable as the
> decision may depend on the resctrl mount options (cdp)
> Squash in arm_mpam: resctrl: Sort the order of the domain lists
> Move out monitor/counter changes to a separate patch
> Commit message update
> ---
> drivers/resctrl/Makefile | 1 +
> drivers/resctrl/mpam_devices.c | 12 ++
> drivers/resctrl/mpam_internal.h | 21 ++
> drivers/resctrl/mpam_resctrl.c | 327 ++++++++++++++++++++++++++++++++
> include/linux/arm_mpam.h | 3 +
> 5 files changed, 364 insertions(+)
> 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 b400a7381d9a..b45743c5fb46 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)) {
> @@ -2516,6 +2522,12 @@ 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 4632985bcca6..28ac501e1ac3 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -12,6 +12,7 @@
> #include <linux/jump_label.h>
> #include <linux/llist.h>
> #include <linux/mutex.h>
> +#include <linux/resctrl.h>
> #include <linux/spinlock.h>
> #include <linux/srcu.h>
> #include <linux/types.h>
> @@ -337,6 +338,16 @@ 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 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;
> @@ -391,6 +402,16 @@ 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..2ffba7a15d6a
> --- /dev/null
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -0,0 +1,327 @@
> +// 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 list of included headers could be simplified since several header files
have been included to mpam_internal.h, for example <linux/arm_mpam.h>,
<linux/cpumask.h>, <asm/mpam.h> and others.

> +/*
> + * 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);
> +
> +bool resctrl_arch_alloc_capable(void)
> +{
> + struct mpam_resctrl_res *res;
> + enum resctrl_res_level rid;
> +
> + for_each_mpam_resctrl_control(res, rid) {
> + if (res->resctrl_res.alloc_capable)
> + return true;
> + }
> +
> + return false;
> +}
> +
> +/*
> + * 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,
> + enum resctrl_res_level rid,
> + struct rdt_domain_hdr *hdr)
> +{
> + lockdep_assert_cpus_held();
> +
> + INIT_LIST_HEAD(&hdr->list);
> + hdr->id = mpam_resctrl_pick_domain_id(cpu, comp);
> + hdr->rid = rid;
> + 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,
^^^
is

> + * 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 void mpam_resctrl_domain_insert(struct list_head *list,
> + struct rdt_domain_hdr *new)
> +{
> + struct rdt_domain_hdr *err;
> + struct list_head *pos = NULL;
> +
> + lockdep_assert_held(&domain_list_lock);
> +
> + err = resctrl_find_domain(list, new->id, &pos);
> + if (WARN_ON_ONCE(err))
> + return;
> +
> + list_add_tail_rcu(&new->list, pos);
> +}
> +
> +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_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 (resctrl_arch_alloc_capable()) {
> + dom->ctrl_comp = ctrl_comp;
> +
> + ctrl_d = &dom->resctrl_ctrl_dom;
> + mpam_resctrl_domain_hdr_init(cpu, ctrl_comp, r->rid, &ctrl_d->hdr);
> + ctrl_d->hdr.type = RESCTRL_CTRL_DOMAIN;
> + err = resctrl_online_ctrl_domain(r, ctrl_d);
> + if (err)
> + goto free_domain;
> +
> + mpam_resctrl_domain_insert(&r->ctrl_domains, &ctrl_d->hdr);
> + } else {
> + pr_debug("Skipped control domain online - no controls\n");
> + }
> + return dom;
> +
> +offline_ctrl_domain:
> + if (resctrl_arch_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 (resctrl_arch_alloc_capable()) {
> + struct rdt_ctrl_domain *ctrl_d = &dom->resctrl_ctrl_dom;
> +
> + mpam_resctrl_online_domain_hdr(cpu, &ctrl_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_ctrl_domain *ctrl_d;
> + bool ctrl_dom_empty;
> +
> + if (!res->class)
> + continue; // dummy resource
> +
> + dom = mpam_resctrl_get_domain_from_cpu(cpu, res);
> + if (WARN_ON_ONCE(!dom))
> + continue;
> +
> + if (resctrl_arch_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 (ctrl_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);
> + 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;
> + }
> +

This pr_debug() could be dropped since @err is set to true only when
a error is returned from mpam_resctrl_control_init(), we already had
a pr_debug() for the reported error.

> + if (!resctrl_arch_alloc_capable()) {
> + pr_debug("No alloc(%u) found - resctrl not supported\n",
> + resctrl_arch_alloc_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.

Thanks,
Gavin