Re: [PATCH v3 6/8] arm_mpam: Add support for memory controller MSC on DT platforms

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] of: memory controller MSC probe failure due to incorrect DT compatible match
- [High] arm_mpam: memory controller MSC accessibility mask left empty due to invalid 'memory' compatible check
--

commit b661da0a277e50a0881896ca5067c92dd25c983b
Author: Shanker Donthineni <sdonthineni@nvidia.com>

arm_mpam: Add support for memory controller MSC on DT platforms

This commit adds support to discover memory-controller MSCs from the device
tree. It derives the component id from the NUMA node, creates a memory class
RIS, and treats a memory parent as accessible from all CPUs.

> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c

[ ... ]

> @@ -2169,6 +2192,8 @@ static void update_msc_accessibility(struct mpam_msc *msc)
>  	} else {
>  		if (of_device_is_compatible(parent, "cache"))
>  			get_cpumask_from_cache(parent, &msc->accessibility);
> +		else if (of_device_is_compatible(parent, "memory"))

[Severity: High]
Does this compatible check actually work for memory nodes?

The of_device_is_compatible() API strictly matches the provided string against
the compatible property array of the device tree node. However, standard
Device Tree memory nodes are identified by device_type = "memory" and do not
have a compatible = "memory" property. Additionally, vendor-specific memory
controllers do not include the generic string "memory" in their compatible
lists.

Since there is no valid node in the kernel with compatible = "memory", will
this check unconditionally fail?

If so, it appears the driver will fall through to the else branch, leave
msc->accessibility uninitialized (empty), and cause the probe to return
-EINVAL, permanently failing the initialization of all memory-class MSCs.

> +			cpumask_copy(&msc->accessibility, cpu_possible_mask);
>  		else
>  			dev_err_once(dev, "Cannot determine accessibility of MSC.\n");
>  	}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261008-mpam-resctrl-dt-knp-support-v3-0-35196c2b43bf@oss.qualcomm.com?part=6