Re: [PATCH v2 06/29] ACPI / MPAM: Parse the MPAM table

James Morse
2025-10-17T18:51:08Z

Hi Fenghua,

On 02/10/2025 04:21, Fenghua Yu wrote:
> On 9/10/25 13:42, James Morse wrote:
>> Add code to parse the arm64 specific MPAM table, looking up the cache
>> level from the PPTT and feeding the end result into the MPAM driver.
>>
>> For now the MPAM hook mpam_ris_create() is stubbed out, but will update
>> the MPAM driver with optional discovered data.

>> diff --git a/drivers/acpi/arm64/mpam.c b/drivers/acpi/arm64/mpam.c
>> new file mode 100644
>> index 000000000000..fd9cfa143676
>> --- /dev/null
>> +++ b/drivers/acpi/arm64/mpam.c

>> +static int acpi_mpam_parse_resource(struct mpam_msc *msc,
>> +                    struct acpi_mpam_resource_node *res)
>> +{
>> +    int level, nid;
>> +    u32 cache_id;
>> +
>> +    switch (res->locator_type) {
>> +    case ACPI_MPAM_LOCATION_TYPE_PROCESSOR_CACHE:
>> +        cache_id = res->locator.cache_locator.cache_reference;
>> +        level = find_acpi_cache_level_from_id(cache_id);
>> +        if (level <= 0) {
>> +            pr_err_once("Bad level (%u) for cache with id %u\n", level, cache_id);
>
> Since level could be negative value here, printing it as %u converts it to positive value
> and will cause debug difficulty. For example, -ENOENT returned by
> find_acpi_cache_level_from_id() will be printed as 4294967294(instead of -2) which is hard
> to know the error code.
>
> Suggest to change this to %d:

Sure, its never meant to be seen!

>             pr_err_once("Bad level (%d) for cache with id %u\n", level, cache_id);
>
>> +            return -EINVAL;
>> +        }
>> +        return mpam_ris_create(msc, res->ris_index, MPAM_CLASS_CACHE,
>> +                       level, cache_id);
>> +    case ACPI_MPAM_LOCATION_TYPE_MEMORY:
>> +        nid = pxm_to_node(res->locator.memory_locator.proximity_domain);
>> +        if (nid == NUMA_NO_NODE)
>> +            nid = 0;
>> +        return mpam_ris_create(msc, res->ris_index, MPAM_CLASS_MEMORY,
>> +                       255, nid);
>> +    default:
>> +        /* These get discovered later and treated as unknown */
>> +        return 0;
>> +    }
>> +}

>> +static bool __init parse_msc_pm_link(struct acpi_mpam_msc_node *tbl_msc,
>> +                     struct platform_device *pdev,
>> +                     u32 *acpi_id)
>> +{
>> +    char hid[sizeof(tbl_msc->hardware_id_linked_device) + 1];
>> +    bool acpi_id_valid = false;
>> +    struct acpi_device *buddy;
>> +    char uid[11];
>> +    int err;
>> +
>> +    memset(&hid, 0, sizeof(hid));
>> +    memcpy(hid, &tbl_msc->hardware_id_linked_device,
>> +           sizeof(tbl_msc->hardware_id_linked_device));
>> +
>> +    if (!strcmp(hid, ACPI_PROCESSOR_CONTAINER_HID)) {
>> +        *acpi_id = tbl_msc->instance_id_linked_device;
>> +        acpi_id_valid = true;
>> +    }
>> +
>> +    err = snprintf(uid, sizeof(uid), "%u",
>> +               tbl_msc->instance_id_linked_device);
>> +    if (err >= sizeof(uid)) {
>
> err could be negative error code.

Not here it can't, from lib/vsprintf.c's documentation of snprintf()
| * The return value is the number of characters which would be
| * generated for the given input, excluding the trailing null,
| * as per ISO C99. If the return is greater than or equal to
| * @size, the resulting string is truncated.

> This error validation only checks size but not error code.
>
> Better to change it to
>
>         if (err < 0 || err >= sizeof(uid))
>

Thanks,

James