[PATCH v2 01/29] ACPI / PPTT: Add a helper to fill a cpumask from a processor container

James Morse
2025-09-10T20:43:34Z

The ACPI MPAM table uses the UID of a processor container specified in
the PPTT to indicate the subset of CPUs and cache topology that can
access each MPAM System Component (MSC).

This information is not directly useful to the kernel. The equivalent
cpumask is needed instead.

Add a helper to find the processor container by its id, then walk
the possible CPUs to fill a cpumask with the CPUs that have this
processor container as a parent.

CC: Dave Martin <dave.martin@arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v1:
* Replaced commit message with wording from Dave.
* Fixed a stray plural.
* Moved further down in the file to make use of get_pptt() helper.
* Added a break to exit the loop early.

Changes since RFC:
* Removed leaf_flag local variable from acpi_pptt_get_cpus_from_container()

Changes since RFC:
* Dropped has_leaf_flag dodging of acpi_pptt_leaf_node()
* Added missing : in kernel-doc
* Made helper return void as this never actually returns an error.
---
drivers/acpi/pptt.c | 83 ++++++++++++++++++++++++++++++++++++++++++++
include/linux/acpi.h | 3 ++
2 files changed, 86 insertions(+)

diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index 54676e3d82dd..1728545d90b2 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -817,3 +817,86 @@ int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
return find_acpi_cpu_topology_tag(cpu, PPTT_ABORT_PACKAGE,
ACPI_PPTT_ACPI_IDENTICAL);
}
+
+/**
+ * acpi_pptt_get_child_cpus() - Find all the CPUs below a PPTT processor node
+ * @table_hdr: A reference to the PPTT table.
+ * @parent_node: A pointer to the processor node in the @table_hdr.
+ * @cpus: A cpumask to fill with the CPUs below @parent_node.
+ *
+ * Walks up the PPTT from every possible CPU to find if the provided
+ * @parent_node is a parent of this CPU.
+ */
+static void acpi_pptt_get_child_cpus(struct acpi_table_header *table_hdr,
+ struct acpi_pptt_processor *parent_node,
+ cpumask_t *cpus)
+{
+ struct acpi_pptt_processor *cpu_node;
+ u32 acpi_id;
+ int cpu;
+
+ cpumask_clear(cpus);
+
+ for_each_possible_cpu(cpu) {
+ acpi_id = get_acpi_id_for_cpu(cpu);
+ cpu_node = acpi_find_processor_node(table_hdr, acpi_id);
+
+ while (cpu_node) {
+ if (cpu_node == parent_node) {
+ cpumask_set_cpu(cpu, cpus);
+ break;
+ }
+ cpu_node = fetch_pptt_node(table_hdr, cpu_node->parent);
+ }
+ }
+}
+
+/**
+ * acpi_pptt_get_cpus_from_container() - Populate a cpumask with all CPUs in a
+ * processor container
+ * @acpi_cpu_id: The UID of the processor container.
+ * @cpus: The resulting CPU mask.
+ *
+ * Find the specified Processor Container, and fill @cpus with all the cpus
+ * below it.
+ *
+ * Not all 'Processor' entries in the PPTT are either a CPU or a Processor
+ * Container, they may exist purely to describe a Private resource. CPUs
+ * have to be leaves, so a Processor Container is a non-leaf that has the
+ * 'ACPI Processor ID valid' flag set.
+ *
+ * Return: 0 for a complete walk, or an error if the mask is incomplete.
+ */
+void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus)
+{
+ struct acpi_pptt_processor *cpu_node;
+ struct acpi_table_header *table_hdr;
+ struct acpi_subtable_header *entry;
+ unsigned long table_end;
+ u32 proc_sz;
+
+ cpumask_clear(cpus);
+
+ table_hdr = acpi_get_pptt();
+ if (!table_hdr)
+ return;
+
+ table_end = (unsigned long)table_hdr + table_hdr->length;
+ entry = ACPI_ADD_PTR(struct acpi_subtable_header, table_hdr,
+ sizeof(struct acpi_table_pptt));
+ proc_sz = sizeof(struct acpi_pptt_processor);
+ while ((unsigned long)entry + proc_sz <= table_end) {
+ cpu_node = (struct acpi_pptt_processor *)entry;
+ if (entry->type == ACPI_PPTT_TYPE_PROCESSOR &&
+ cpu_node->flags & ACPI_PPTT_ACPI_PROCESSOR_ID_VALID) {
+ if (!acpi_pptt_leaf_node(table_hdr, cpu_node)) {
+ if (cpu_node->acpi_processor_id == acpi_cpu_id) {
+ acpi_pptt_get_child_cpus(table_hdr, cpu_node, cpus);
+ break;
+ }
+ }
+ }
+ entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry,
+ entry->length);
+ }
+}
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 1c5bb1e887cd..f97a9ff678cc 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1541,6 +1541,7 @@ int find_acpi_cpu_topology(unsigned int cpu, int level);
int find_acpi_cpu_topology_cluster(unsigned int cpu);
int find_acpi_cpu_topology_package(unsigned int cpu);
int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
+void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus);
#else
static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
{
@@ -1562,6 +1563,8 @@ static inline int find_acpi_cpu_topology_hetero_id(unsigned int cpu)
{
return -EINVAL;
}
+static inline void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id,
+ cpumask_t *cpus) { }
#endif

void acpi_arch_init(void);
--
2.39.5