Re: [PATCH 01/33] ACPI / PPTT: Add a helper to fill a cpumask from a processor container

Gavin Shan
2025-11-08T04:31:47Z

Hi Ben,

On 11/7/25 10:34 PM, Ben Horgan wrote:
> From: James Morse <james.morse@arm.com>
>
> 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>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Fenghua Yu <fenghuay@nvidia.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
> Tested-by: Peter Newman <peternewman@google.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
> Changes since v3:
> Refer to processor hierarchy in comments (Jonathan)
> Fix indent (Jonathan)
> ---
> drivers/acpi/pptt.c | 85 ++++++++++++++++++++++++++++++++++++++++++++
> include/linux/acpi.h | 3 ++
> 2 files changed, 88 insertions(+)
>

Two nitpicks below...

> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 54676e3d82dd..69917cc6bd2f 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -817,3 +817,88 @@ 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 hierarchy node
> + *
> + * @table_hdr: A reference to the PPTT table
> + * @parent_node: A pointer to the processor hierarchy 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 Hierarchy' 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.
> + */
> +void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus)
> +{
> + 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) {
> +

Unnecessary blank line here.

> + if (entry->type == ACPI_PPTT_TYPE_PROCESSOR) {
> + struct acpi_pptt_processor *cpu_node;
> +
> + cpu_node = (struct acpi_pptt_processor *)entry;
> + if (cpu_node->flags & ACPI_PPTT_ACPI_PROCESSOR_ID_VALID &&
> + !acpi_pptt_leaf_node(table_hdr, cpu_node) &&
> + 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);

Need we to check if @cpu_node does crosses the boundary (@table_end), as what's
doing in acpi_find_processor_node()? Actually, the similar hunk of code from
the function can be reused here.

static struct acpi_pptt_processor *acpi_find_processor_node(struct acpi_table_header *table_hdr,
u32 acpi_cpu_id)
{
:
while ((unsigned long)entry + proc_sz <= table_end) {
cpu_node = (struct acpi_pptt_processor *)entry;

if (entry->length == 0) {
pr_warn("Invalid zero length subtable\n");
break;
}

/* entry->length may not equal proc_sz, revalidate the processor structure length */
if (entry->type == ACPI_PPTT_TYPE_PROCESSOR &&
acpi_cpu_id == cpu_node->acpi_processor_id &&
(unsigned long)entry + entry->length <= table_end &&
entry->length == proc_sz + cpu_node->number_of_priv_resources * sizeof(u32) &&
acpi_pptt_leaf_node(table_hdr, cpu_node)) {
return (struct acpi_pptt_processor *)entry;
}

entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry,
entry->length);
}

:
}

> + }
> +}
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 5ff5d99f6ead..4752ebd48132 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);

Thanks,
Gavin