Re: [PATCH 4/6] firmware: arm_rmm: Configure the RMM with the host's page size

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Missing validation of RMM granule size against cached feature registers.
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--- Patch [4]: [PATCH 4/6] firmware: arm_rmm: Configure the RMM with the host's page size ---
commit db91734b5b3e860f7a56847c4c9ab7f969eaf312
Author: Steven Price <steven.price@arm.com>

firmware: arm_rmm: Configure the RMM with the host's page size

This commit introduces a function to configure the RMM's granule size to match
the host's page size. It allocates a configuration page, populates the
rmi_granule_size according to PAGE_SIZE, and calls rmi_rmm_config_set() to
apply the settings.

> diff --git a/drivers/firmware/arm_rmm/rmi.c b/drivers/firmware/arm_rmm/rmi.c
> index c4850976544ff..e7ab4a7df3ca8 100644
> --- a/drivers/firmware/arm_rmm/rmi.c
> +++ b/drivers/firmware/arm_rmm/rmi.c
[ ... ]
> @@ -76,6 +76,45 @@ static int rmi_read_features(void)
>  	return 0;
>  }
>  
> +static int rmi_configure(void)
> +{
> +	unsigned long ret;
> +	struct rmm_config *config __free(free_page) = (struct rmm_config *)get_zeroed_page(GFP_KERNEL);
> +
> +	if (!config)
> +		return -ENOMEM;
> +
> +	switch (PAGE_SIZE) {

[Severity: Medium]
The commit message states "Check the feature registers and configure the
RMM so that it matches the host's page size."

Does rmi_configure() actually verify the host's PAGE_SIZE against the
cached RMM feature registers before proceeding?

It appears to unconditionally assign the configuration based on PAGE_SIZE.
If the RMM does not support the host's page size, the driver will blindly
send an unsupported configuration to the RMM firmware.

Should there be a validation check here using the features read in
rmi_read_features() before configuring the granule size?

> +	case SZ_4K:
> +		config->rmi_granule_size = RMI_GRANULE_SIZE_4KB;
> +		break;
> +	case SZ_16K:
> +		config->rmi_granule_size = RMI_GRANULE_SIZE_16KB;
> +		break;
> +	case SZ_64K:
> +		config->rmi_granule_size = RMI_GRANULE_SIZE_64KB;
> +		break;
> +	default:
> +		BUILD_BUG();
> +	}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260715142739.80398-1-steven.price@arm.com?part=4