Re: [PATCH v17 3/7] firmware: arm_rmm: Configure the RMM with the host's page size

[Gavin Shan <gshan@redhat.com>]

Hi Suzuki,

On 9/7/26 7:59 PM, Suzuki K Poulose wrote:
> From: Steven Price <steven.price@arm.com>
> 
> RMM v2.0 brings the ability to set the RMM's granule size. Check the
> feature registers and configure the RMM so that it matches the host's
> page size. This means that operations can be done with a granularity
> equal to PAGE_SIZE.
> 
> Signed-off-by: Steven Price <steven.price@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
>   Changes since v15:
>    * Actually check the feature register for the host's page-size support.
>   Changes since v14:
>    * Move the implementation into drivers/firmware/arm_rmm.
>   Changes since v13:
>    * Moved out of KVM.
> ---
>   drivers/firmware/arm_rmm/rmi.c | 58 ++++++++++++++++++++++++++++++++++
>   include/linux/arm-rmi-cmds.h   | 17 ++++++++++
>   2 files changed, 75 insertions(+)
> 
> diff --git a/drivers/firmware/arm_rmm/rmi.c b/drivers/firmware/arm_rmm/rmi.c
> index 008a783407b4e..76f91c145e1fd 100644
> --- a/drivers/firmware/arm_rmm/rmi.c
> +++ b/drivers/firmware/arm_rmm/rmi.c
> @@ -77,6 +77,60 @@ static int rmi_read_features(void)
>   	return 0;
>   }
>   
> +static int rmi_configure(void)
> +{
> +	unsigned long granule_feature;
> +	unsigned long granule_size;
> +	int ret = 0;
> +	struct rmm_config *config;
> +
> +	switch (PAGE_SIZE) {
> +	case SZ_4K:
> +		granule_size = RMI_GRANULE_SIZE_4KB;
> +		granule_feature = RMI_FEATURE_REGISTER_1_RMI_GRAN_SZ_4KB;
> +		break;
> +	case SZ_16K:
> +		granule_size = RMI_GRANULE_SIZE_16KB;
> +		granule_feature = RMI_FEATURE_REGISTER_1_RMI_GRAN_SZ_16KB;
> +		break;
> +	case SZ_64K:
> +		granule_size = RMI_GRANULE_SIZE_64KB;
> +		granule_feature = RMI_FEATURE_REGISTER_1_RMI_GRAN_SZ_64KB;
> +		break;
> +	default:
> +		BUILD_BUG();
> +	}
> +
> +	if (!(rmi_feat_reg(1) & granule_feature)) {
> +		pr_err("RMM does not support %luKB granules\n",
> +		       PAGE_SIZE >> 10);
> +		return -ENXIO;
> +	}
> +
> +	config = (struct rmm_config *)get_zeroed_page(GFP_KERNEL);
> +	if (!config)
> +		return -ENOMEM;

An error message is needed here.

	if (!config) {
		pr_err("Unable to alloc RMM config memory\n");
		return -ENOMEM;
	}

> +
> +	config->rmi_granule_size = granule_size;
> +
> +	/*
> +	 * For now we set the tracking_region_size to 0 which is the only option
> +	 * for 4KB PAGE_SIZE (1GB for 4KB PAGE_SIZE, 32MB/512MB for 16KB/64KB).
> +	 * TODO: Support other tracking sizes via Kconfig option for other
> +	 * PAGE_SIZES
> +	 */
> +	config->tracking_region_size = 0;
> +
> +	ret = rmi_rmm_config_set(virt_to_phys(config));
> +	if (ret) {
> +		pr_err("RMM config set failed\n");
> +		ret = -EINVAL;
> +	}

The error code from rmi_rmm_config_set() is indicative sometimes. Also, -ENXIO
would be more appropriate than -EINVAL?

	if (ret) {
		pr_err("RMM config set failed (%d)\n", ret);
		ret = -ENXIO;
	}

> +
> +	free_page((unsigned long)config);
> +	return ret;
> +}
> +
>   static int __init arm64_init_rmi(void)
>   {
>   	int ret;
> @@ -90,6 +144,10 @@ static int __init arm64_init_rmi(void)
>   	if (ret)
>   		return ret;
>   
> +	ret = rmi_configure();
> +	if (ret)
> +		return ret;
> +
>   	return 0;
>   }
>   
> diff --git a/include/linux/arm-rmi-cmds.h b/include/linux/arm-rmi-cmds.h
> index 2fb1f7f86d71e..9aa27697e2377 100644
> --- a/include/linux/arm-rmi-cmds.h
> +++ b/include/linux/arm-rmi-cmds.h
> @@ -12,6 +12,23 @@
>   
>   unsigned long rmi_feat_reg(unsigned long id);
>   
> +/**
> + * rmi_rmm_config_set() - Configure the RMM
> + * @cfg_ptr: PA of a struct rmm_config
> + *
> + * Sets configuration options on the RMM.
> + *
> + * Return: RMI return code
> + */
> +static inline int rmi_rmm_config_set(unsigned long cfg_ptr)
> +{
> +	struct arm_smccc_res res;
> +
> +	arm_smccc_1_1_invoke(SMC_RMI_RMM_CONFIG_SET, cfg_ptr, &res);
> +
> +	return res.a0;
> +}
> +

rmi_rmm_config_set() is used for once by rmi.c::rmi_configure(), I would not expose
rmi_rmm_config_set() by combining the logic to rmi.c::rmi_configure().

>   /**
>    * rmi_features() - Read feature register
>    * @index: Feature register index

Thanks,
Gavin