Hi Gavin,

On 11/9/25 00:07, Gavin Shan wrote:

Hi Ben,

On 11/7/25 10:34 PM, Ben Horgan wrote:

quoted

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

An MSC is a container of resources, each identified by their RIS index.
Some RIS are described by firmware to provide their position in the
system.
Others are discovered when the driver probes the hardware.

To configure a resource it needs to be found by its class, e.g. 'L2'.
There are two kinds of grouping, a class is a set of components, which
are visible to user-space as there are likely to be multiple instances
of the L2 cache. (e.g. one per cluster or package)

Add support for creating and destroying structures to allow a hierarchy
of resources to be created.

CC: Ben Horgan <ben.horgan@arm.com>
Tested-by: Fenghua Yu <fenghuay@nvidia.com>
Tested-by: Shaopeng Tan <redacted>
Tested-by: Peter Newman <redacted>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since v3:
Jonathan:
Code reordering.
Comments.
---
  drivers/resctrl/mpam_devices.c  | 393 +++++++++++++++++++++++++++++++-
  drivers/resctrl/mpam_internal.h |  94 ++++++++
  include/linux/arm_mpam.h        |   5 +
  3 files changed, 491 insertions(+), 1 deletion(-)

Some minor comments below and some of them may be invalid. Nothing really
looks incorrect to me:

Reviewed-by: Gavin Shan <redacted>

quoted

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/

mpam_devices.c
index 6c6be133d73a..48a344d5cb43 100644

--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c

@@ -36,6 +36,384 @@ struct srcu_struct mpam_srcu;

   */
  static atomic_t mpam_num_msc;
  +/*
+ * An MSC is a physical container for controls and monitors, each
identified by
+ * their RIS index. These share a base-address, interrupts and some MMIO
+ * registers. A vMSC is a virtual container for RIS in an MSC that
control or
+ * monitor the same thing. Members of a vMSC are all RIS in the same
MSC, but
+ * not all RIS in an MSC share a vMSC.

s/a virtual container for RIS/a virtual container for RISes
s/all RIS/all RISes

The comments/message in the driver treat RIS is as an invariable noun;
that is the singular and plural are the same. This makes sense when read
out loud. I'll keep it as is unless you think making a singular/plural
disctinction makes it significantly easier to understand.

An empty line may be needed here as paragraph separator.

Done

quoted

+ * Components are a group of vMSC that control or monitor the same
thing but
+ * are from different MSC, so have different base-address, interrupts
etc.
+ * Classes are the set components of the same type.
+ *
+ * The features of a vMSC is the union of the RIS it contains.
+ * The features of a Class and Component are the common subset of the
vMSC
+ * they contain.
+ *

s/the RIS/the RISes

quoted

+ * e.g. The system cache may have bandwidth controls on multiple
interfaces,
+ * for regulating traffic from devices independently of traffic from
CPUs.
+ * If these are two RIS in one MSC, they will be treated as controlling
+ * different things, and will not share a vMSC/component/class.
+ *
+ * e.g. The L2 may have one MSC and two RIS, one for cache-controls
another
+ * for bandwidth. These two RIS are members of the same vMSC.
+ *
+ * e.g. The set of RIS that make up the L2 are grouped as a
component. These
+ * are sometimes termed slices. They should be configured the same,
as if there
+ * were only one.
+ *
+ * e.g. The SoC probably has more than one L2, each attached to a
distinct set
+ * of CPUs. All the L2 components are grouped as a class.
+ *
+ * When creating an MSC, struct mpam_msc is added to the all
mpam_all_msc list,
+ * then linked via struct mpam_ris to a vmsc, component and class.
+ * The same MSC may exist under different class->component->vmsc
paths, but the
+ * RIS index will be unique.
+ */
+LIST_HEAD(mpam_classes);
+
+/* List of all objects that can be free()d after synchronise_srcu() */
+static LLIST_HEAD(mpam_garbage);
+
+static inline void init_garbage(struct mpam_garbage *garbage)
+{
+    init_llist_node(&garbage->llist);
+}
+
+#define add_to_garbage(x)                \
+do {                            \
+    __typeof__(x) _x = (x);                \
+    _x->garbage.to_free = _x;            \
+    llist_add(&_x->garbage.llist, &mpam_garbage);    \
+} while (0)
+
+static void mpam_free_garbage(void)
+{
+    struct mpam_garbage *iter, *tmp;
+    struct llist_node *to_free = llist_del_all(&mpam_garbage);
+
+    if (!to_free)
+        return;
+
+    synchronize_srcu(&mpam_srcu);
+
+    llist_for_each_entry_safe(iter, tmp, to_free, llist) {
+        if (iter->pdev)
+            devm_kfree(&iter->pdev->dev, iter->to_free);
+        else
+            kfree(iter->to_free);
+    }
+}
+
+static struct mpam_vmsc *
+mpam_vmsc_alloc(struct mpam_component *comp, struct mpam_msc *msc)
+{
+    struct mpam_vmsc *vmsc;
+
+    lockdep_assert_held(&mpam_list_lock);
+
+    vmsc = kzalloc(sizeof(*vmsc), GFP_KERNEL);
+    if (!vmsc)
+        return ERR_PTR(-ENOMEM);
+    init_garbage(&vmsc->garbage);
+
+    INIT_LIST_HEAD_RCU(&vmsc->ris);
+    INIT_LIST_HEAD_RCU(&vmsc->comp_list);
+    vmsc->comp = comp;
+    vmsc->msc = msc;
+
+    list_add_rcu(&vmsc->comp_list, &comp->vmsc);
+
+    return vmsc;
+}
+
+static void mpam_component_destroy(struct mpam_component *comp);
+
+static void mpam_vmsc_destroy(struct mpam_vmsc *vmsc)
+{
+    struct mpam_component *comp = vmsc->comp;
+
+    lockdep_assert_held(&mpam_list_lock);
+
+    list_del_rcu(&vmsc->comp_list);
+    add_to_garbage(vmsc);
+
+    if (list_empty(&comp->vmsc))
+        mpam_component_destroy(comp);
+}
+
+static struct mpam_vmsc *
+mpam_vmsc_find(struct mpam_component *comp, struct mpam_msc *msc)
+{
+    struct mpam_vmsc *vmsc;
+
+    lockdep_assert_held(&mpam_list_lock);
+
+    list_for_each_entry(vmsc, &comp->vmsc, comp_list) {
+        if (vmsc->msc->id == msc->id)
+            return vmsc;
+    }
+
+    return mpam_vmsc_alloc(comp, msc);
+}
+
+static struct mpam_component *
+mpam_component_alloc(struct mpam_class *class, int id)
+{
+    struct mpam_component *comp;
+
+    lockdep_assert_held(&mpam_list_lock);
+
+    comp = kzalloc(sizeof(*comp), GFP_KERNEL);
+    if (!comp)
+        return ERR_PTR(-ENOMEM);
+    init_garbage(&comp->garbage);
+
+    comp->comp_id = id;
+    INIT_LIST_HEAD_RCU(&comp->vmsc);
+    /* affinity is updated when ris are added */

    /* Affinity is updated when RIS is added */

quoted

+    INIT_LIST_HEAD_RCU(&comp->class_list);
+    comp->class = class;
+
+    list_add_rcu(&comp->class_list, &class->components);
+
+    return comp;
+}
+
+static void mpam_class_destroy(struct mpam_class *class);
+
+static void mpam_component_destroy(struct mpam_component *comp)
+{
+    struct mpam_class *class = comp->class;
+
+    lockdep_assert_held(&mpam_list_lock);
+
+    list_del_rcu(&comp->class_list);
+    add_to_garbage(comp);
+
+    if (list_empty(&class->components))
+        mpam_class_destroy(class);
+}
+
+static struct mpam_component *
+mpam_component_find(struct mpam_class *class, int id)
+{
+    struct mpam_component *comp;
+
+    lockdep_assert_held(&mpam_list_lock);
+
+    list_for_each_entry(comp, &class->components, class_list) {
+        if (comp->comp_id == id)
+            return comp;
+    }
+
+    return mpam_component_alloc(class, id);
+}
+
+static struct mpam_class *
+mpam_class_alloc(u8 level_idx, enum mpam_class_types type)
+{
+    struct mpam_class *class;
+
+    lockdep_assert_held(&mpam_list_lock);
+
+    class = kzalloc(sizeof(*class), GFP_KERNEL);
+    if (!class)
+        return ERR_PTR(-ENOMEM);
+    init_garbage(&class->garbage);
+
+    INIT_LIST_HEAD_RCU(&class->components);
+    /* affinity is updated when ris are added */

    /* Affinity is updated when RIS is added */

quoted

+    class->level = level_idx;
+    class->type = type;
+    INIT_LIST_HEAD_RCU(&class->classes_list);
+
+    list_add_rcu(&class->classes_list, &mpam_classes);
+
+    return class;
+}
+
+static void mpam_class_destroy(struct mpam_class *class)
+{
+    lockdep_assert_held(&mpam_list_lock);
+
+    list_del_rcu(&class->classes_list);
+    add_to_garbage(class);
+}
+
+static struct mpam_class *
+mpam_class_find(u8 level_idx, enum mpam_class_types type)
+{
+    struct mpam_class *class;
+
+    lockdep_assert_held(&mpam_list_lock);
+
+    list_for_each_entry(class, &mpam_classes, classes_list) {
+        if (class->type == type && class->level == level_idx)
+            return class;
+    }
+
+    return mpam_class_alloc(level_idx, type);
+}
+
+/*
+ * The cacheinfo structures are only populated when CPUs are online.
+ * This helper walks the acpi tables to include offline CPUs too.
+ */
+int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32
cache_level,
+                   cpumask_t *affinity)
+{
+    return acpi_pptt_get_cpumask_from_cache_id(cache_id, affinity);
+}
+

This function is only used in mpam_devices.c and won't be exposed in the
future, we can make it 'static' and 'inline'.

Done

quoted

+/*
+ * cpumask_of_node() only knows about online CPUs. This can't tell us
whether
+ * a class is represented on all possible CPUs.
+ */
+static void get_cpumask_from_node_id(u32 node_id, cpumask_t *affinity)
+{
+    int cpu;
+
+    for_each_possible_cpu(cpu) {
+        if (node_id == cpu_to_node(cpu))
+            cpumask_set_cpu(cpu, affinity);
+    }
+}
+
+static int mpam_ris_get_affinity(struct mpam_msc *msc, cpumask_t
*affinity,
+                 enum mpam_class_types type,
+                 struct mpam_class *class,
+                 struct mpam_component *comp)
+{
+    int err;
+
+    switch (type) {
+    case MPAM_CLASS_CACHE:
+        err = mpam_get_cpumask_from_cache_id(comp->comp_id, class-

quoted

level,

+                             affinity);
+        if (err)
+            return err;

It's worthy to add a warning message here.

Added: Failed to determine CPU affinity

quoted

+
+        if (cpumask_empty(affinity))
+            dev_warn_once(&msc->pdev->dev,
+                      "no CPUs associated with cache node\n");

{} is needed here.

Made it one line.

quoted

+
+        break;
+    case MPAM_CLASS_MEMORY:
+        get_cpumask_from_node_id(comp->comp_id, affinity);
+        /* affinity may be empty for CPU-less memory nodes */
+        break;
+    case MPAM_CLASS_UNKNOWN:
+        return 0;
+    }
+
+    cpumask_and(affinity, affinity, &msc->accessibility);
+
+    return 0;
+}
+
+static int mpam_ris_create_locked(struct mpam_msc *msc, u8 ris_idx,
+                  enum mpam_class_types type, u8 class_id,
+                  int component_id)
+{
+    int err;
+    struct mpam_vmsc *vmsc;
+    struct mpam_msc_ris *ris;
+    struct mpam_class *class;
+    struct mpam_component *comp;
+    struct platform_device *pdev = msc->pdev;
+
+    lockdep_assert_held(&mpam_list_lock);
+
+    if (ris_idx > MPAM_MSC_MAX_NUM_RIS)
+        return -EINVAL;
+
+    if (test_and_set_bit(ris_idx, &msc->ris_idxs))
+        return -EBUSY;
+
+    ris = devm_kzalloc(&msc->pdev->dev, sizeof(*ris), GFP_KERNEL);
+    if (!ris)
+        return -ENOMEM;
+    init_garbage(&ris->garbage);
+    ris->garbage.pdev = pdev;
+
+    class = mpam_class_find(class_id, type);
+    if (IS_ERR(class))
+        return PTR_ERR(class);
+
+    comp = mpam_component_find(class, component_id);
+    if (IS_ERR(comp)) {
+        if (list_empty(&class->components))
+            mpam_class_destroy(class);
+        return PTR_ERR(comp);
+    }
+
+    vmsc = mpam_vmsc_find(comp, msc);
+    if (IS_ERR(vmsc)) {
+        if (list_empty(&comp->vmsc))
+            mpam_component_destroy(comp);
+        return PTR_ERR(vmsc);
+    }
+
+    err = mpam_ris_get_affinity(msc, &ris->affinity, type, class, comp);
+    if (err) {
+        if (list_empty(&vmsc->ris))
+            mpam_vmsc_destroy(vmsc);
+        return err;
+    }
+
+    ris->ris_idx = ris_idx;
+    INIT_LIST_HEAD_RCU(&ris->msc_list);
+    INIT_LIST_HEAD_RCU(&ris->vmsc_list);
+    ris->vmsc = vmsc;
+
+    cpumask_or(&comp->affinity, &comp->affinity, &ris->affinity);
+    cpumask_or(&class->affinity, &class->affinity, &ris->affinity);
+    list_add_rcu(&ris->vmsc_list, &vmsc->ris);
+    list_add_rcu(&ris->msc_list, &msc->ris);
+
+    return 0;
+}
+
+static void mpam_ris_destroy(struct mpam_msc_ris *ris)
+{
+    struct mpam_vmsc *vmsc = ris->vmsc;
+    struct mpam_msc *msc = vmsc->msc;
+    struct mpam_component *comp = vmsc->comp;
+    struct mpam_class *class = comp->class;
+
+    lockdep_assert_held(&mpam_list_lock);
+
+    /*
+     * It is assumed affinities don't overlap. If they do the class
becomes
+     * unusable immediately.
+     */
+    cpumask_andnot(&class->affinity, &class->affinity, &ris->affinity);
+    cpumask_andnot(&comp->affinity, &comp->affinity, &ris->affinity);
+    clear_bit(ris->ris_idx, &msc->ris_idxs);
+    list_del_rcu(&ris->msc_list);
+    list_del_rcu(&ris->vmsc_list);
+    add_to_garbage(ris);
+
+    if (list_empty(&vmsc->ris))
+        mpam_vmsc_destroy(vmsc);
+}
+
+int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
+            enum mpam_class_types type, u8 class_id, int component_id)
+{
+    int err;
+
+    mutex_lock(&mpam_list_lock);
+    err = mpam_ris_create_locked(msc, ris_idx, type, class_id,
+                     component_id);
+    mutex_unlock(&mpam_list_lock);
+    if (err)
+        mpam_free_garbage();
+
+    return err;
+}
+
  /*
   * An MSC can control traffic from a set of CPUs, but may only be
accessible
   * from a (hopefully wider) set of CPUs. The common reason for this
is power

@@ -60,14 +438,25 @@ static int update_msc_accessibility(struct

mpam_msc *msc)
    static int fw_num_msc;
  +/*
+ * There are two ways of reaching a struct mpam_msc_ris. Via the
+ * class->component->vmsc->ris, or via the msc.
+ * When destroying the msc, the other side needs unlinking and
cleaning up too.
+ */
  static void mpam_msc_destroy(struct mpam_msc *msc)
  {
      struct platform_device *pdev = msc->pdev;
+    struct mpam_msc_ris *ris, *tmp;
        lockdep_assert_held(&mpam_list_lock);
  +    list_for_each_entry_safe(ris, tmp, &msc->ris, msc_list)
+        mpam_ris_destroy(ris);
+
      list_del_rcu(&msc->all_msc_list);
      platform_set_drvdata(pdev, NULL);
+
+    add_to_garbage(msc);
  }
    static void mpam_msc_drv_remove(struct platform_device *pdev)

@@ -81,7 +470,7 @@ static void mpam_msc_drv_remove(struct

platform_device *pdev)
      mpam_msc_destroy(msc);
      mutex_unlock(&mpam_list_lock);
  -    synchronize_srcu(&mpam_srcu);
+    mpam_free_garbage();
  }
    static struct mpam_msc *do_mpam_msc_drv_probe(struct
platform_device *pdev)

@@ -97,6 +486,8 @@ static struct mpam_msc

*do_mpam_msc_drv_probe(struct platform_device *pdev)
      msc = devm_kzalloc(&pdev->dev, sizeof(*msc), GFP_KERNEL);
      if (!msc)
          return ERR_PTR(-ENOMEM);
+    init_garbage(&msc->garbage);
+    msc->garbage.pdev = pdev;
        err = devm_mutex_init(dev, &msc->probe_lock);
      if (err)

diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/

mpam_internal.h
index 540066903eca..8f7a28d2c021 100644

--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h

@@ -7,11 +7,30 @@

  #include <linux/arm_mpam.h>
  #include <linux/cpumask.h>
  #include <linux/io.h>
+#include <linux/llist.h>
  #include <linux/mutex.h>
+#include <linux/srcu.h>
  #include <linux/types.h>
  +#define MPAM_MSC_MAX_NUM_RIS    16
+
  struct platform_device;
  +/*
+ * Structures protected by SRCU may not be freed for a surprising
amount of
+ * time (especially if perf is running). To ensure the MPAM error
interrupt can
+ * tear down all the structures, build a list of objects that can be
garbage
+ * collected once synchronize_srcu() has returned.
+ * If pdev is non-NULL, use devm_kfree().
+ */
+struct mpam_garbage {
+    /* member of mpam_garbage */
+    struct llist_node    llist;
+
+    void            *to_free;
+    struct platform_device    *pdev;
+};
+
  struct mpam_msc {
      /* member of mpam_all_msc */
      struct list_head    all_msc_list;

@@ -45,5 +64,80 @@ struct mpam_msc {

        void __iomem        *mapped_hwpage;
      size_t            mapped_hwpage_sz;
+
+    struct mpam_garbage    garbage;
+};
+
+struct mpam_class {
+    /* mpam_components in this class */
+    struct list_head    components;
+
+    cpumask_t        affinity;
+
+    u8            level;
+    enum mpam_class_types    type;
+
+    /* member of mpam_classes */
+    struct list_head    classes_list;
+
+    struct mpam_garbage    garbage;
+};
+
+struct mpam_component {
+    u32            comp_id;
+
+    /* mpam_vmsc in this component */
+    struct list_head    vmsc;
+
+    cpumask_t        affinity;
+
+    /* member of mpam_class:components */
+    struct list_head    class_list;
+
+    /* parent: */
+    struct mpam_class    *class;
+
+    struct mpam_garbage    garbage;
+};
+
+struct mpam_vmsc {
+    /* member of mpam_component:vmsc_list */
+    struct list_head    comp_list;
+
+    /* mpam_msc_ris in this vmsc */
+    struct list_head    ris;
+
+    /* All RIS in this vMSC are members of this MSC */
+    struct mpam_msc        *msc;
+
+    /* parent: */
+    struct mpam_component    *comp;
+
+    struct mpam_garbage    garbage;
+};
+
+struct mpam_msc_ris {
+    u8            ris_idx;
+
+    cpumask_t        affinity;
+
+    /* member of mpam_vmsc:ris */
+    struct list_head    vmsc_list;
+
+    /* member of mpam_msc:ris */
+    struct list_head    msc_list;
+
+    /* parent: */
+    struct mpam_vmsc    *vmsc;
+
+    struct mpam_garbage    garbage;
  };
+
+/* List of all classes - protected by srcu*/
+extern struct srcu_struct mpam_srcu;
+extern struct list_head mpam_classes;
+
+int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32
cache_level,
+                   cpumask_t *affinity);
+
  #endif /* MPAM_INTERNAL_H */

diff --git a/include/linux/arm_mpam.h b/include/linux/arm_mpam.h
index a3828ef91aee..5a3aab6bb1d4 100644
--- a/include/linux/arm_mpam.h
+++ b/include/linux/arm_mpam.h

@@ -37,11 +37,16 @@ static inline int acpi_mpam_parse_resources(struct

mpam_msc *msc,
  static inline int acpi_mpam_count_msc(void) { return -EINVAL; }
  #endif
  +#ifdef CONFIG_ARM64_MPAM_DRIVER
+int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
+            enum mpam_class_types type, u8 class_id, int component_id);
+#else
  static inline int mpam_ris_create(struct mpam_msc *msc, u8 ris_idx,
                    enum mpam_class_types type, u8 class_id,
                    int component_id)
  {
      return -EINVAL;
  }
+#endif
    #endif /* __LINUX_ARM_MPAM_H */

Thanks,
Gavin

-- 
Thanks,

Ben