Re: [PATCH 1/4] ACPI / PPTT: Add a helper to fill a cpumask from a processor container

[James Morse <james.morse@arm.com>]

Hello!

(CC: +Dave Martin)

On 12/06/2025 18:13, James Morse wrote:
> The PPTT describes CPUs and caches, as well as processor containers.
> The ACPI table for MPAM describes the set of CPUs that can access an MSC
> with the UID of a processor container.
> 
> 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.

> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 54676e3d82dd..aaf9b5a26d07 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -298,6 +298,97 @@ static struct acpi_pptt_processor *acpi_find_processor_node(struct acpi_table_he

> +/**
> + * acpi_pptt_get_cpus_from_container() - Populate a cpumask with all CPUs in a
> + *                                       processor containers
> + * @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.
> + */
> +int 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;
> +	bool leaf_flag, has_leaf_flag = false;
> +	unsigned long table_end;
> +	acpi_status status;
> +	u32 proc_sz;
> +	int ret = 0;
> +
> +	cpumask_clear(cpus);
> +
> +	status = acpi_get_table(ACPI_SIG_PPTT, 0, &table_hdr);
> +	if (ACPI_FAILURE(status))
> +		return 0;
> +
> +	if (table_hdr->revision > 1)
> +		has_leaf_flag = true;
> +
> +	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) {

Dave Martin picked out an off-by-one here - this pattern was copied from other functions,
then fixed while I was still lugging this around out of tree. Should be:
|       while ((unsigned long)entry + proc_sz <= table_end) {

See adfab6b39202481bb43286fff94def4953793fdb.

I've fixed this locally.


> +		cpu_node = (struct acpi_pptt_processor *)entry;
> +		if (entry->type == ACPI_PPTT_TYPE_PROCESSOR &&
> +		    cpu_node->flags & ACPI_PPTT_ACPI_PROCESSOR_ID_VALID) {
> +			leaf_flag = cpu_node->flags & ACPI_PPTT_ACPI_LEAF_NODE;
> +			if ((has_leaf_flag && !leaf_flag) ||
> +			    (!has_leaf_flag && !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);
> +			}
> +		}
> +		entry = ACPI_ADD_PTR(struct acpi_subtable_header, entry,
> +				     entry->length);
> +	}
> +
> +	acpi_put_table(table_hdr);
> +
> +	return ret;
> +}


Thanks,

James