Re: [PATCH v3 7/8] arm_mpam: Support MSC accessibility derivation from RIS nodes

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] arm_mpam: Mismatch in RIS node iteration causes childless MSC nodes to fail probe
--

commit 6ccd46129e50bd63d07916d508a9533280b06972
Author: Yin Li <yin.li@oss.qualcomm.com>

arm_mpam: Support MSC accessibility derivation from RIS nodes

This commit adds a per-RIS fallback path for resolving an MSC's CPU affinity
when the parent node does not provide an affinity hint. It factors the
device tree specific logic into mpam_dt_update_msc_accessibility().

> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 048d32e69f55f..80157b819c3d1 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c

[ ... ]

> +static void mpam_dt_update_msc_accessibility(struct mpam_msc *msc)
> +{
> +	cpumask_t *affinity = &msc->accessibility;
> +
> +	cpumask_clear(affinity);
> +
> +	if (get_cpumask_from_parent(msc, affinity) == -ENODEV) {
> +		for_each_available_child_of_node_scoped(msc->pdev->dev.of_node, ris) {
> +			if (get_cpumask_from_ris(ris, affinity)) {
> +				cpumask_clear(affinity);
> +				break;
> +			}
> +		}
> +	}
> +}

[Severity: High]
Does this code introduce a regression for MSC nodes without child RIS nodes?

In mpam_dt_parse_resources(), childless MSC nodes are supported by explicitly
using the MSC node itself as the RIS if no children are found.

However, in this new fallback path, if get_cpumask_from_parent() returns
-ENODEV and the MSC node has no children, the
for_each_available_child_of_node_scoped() loop will not execute. This leaves
the affinity mask empty and causes the driver to abort the probe since the MSC
is not accessible from any CPU.

Additionally, does this loop iterate all child nodes without verifying they are
actually RIS nodes?

By not checking for a reg property, any non-RIS child node could cause
get_cpumask_from_ris() to fail, which clears the affinity mask and spuriously
aborts the probe.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261008-mpam-resctrl-dt-knp-support-v3-0-35196c2b43bf@oss.qualcomm.com?part=7