Re: [PATCH v18 3/7] firmware: arm_rmm: Configure the RMM with the host's page size

[Gavin Shan <gshan@redhat.com>]

On 9/12/26 6:36 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.
> 
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Steven Price <steven.price@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
>   Changes since v17:
>    * Move rmi_config_set() out of the header file.
>    * Print the error message for rmi_config_set if it fails
>   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 | 79 ++++++++++++++++++++++++++++++++++
>   1 file changed, 79 insertions(+)
> 
> diff --git a/drivers/firmware/arm_rmm/rmi.c b/drivers/firmware/arm_rmm/rmi.c
> index 2fd538c937dca..5b0e342ce3d58 100644
> --- a/drivers/firmware/arm_rmm/rmi.c
> +++ b/drivers/firmware/arm_rmm/rmi.c
> @@ -35,6 +35,25 @@ static int rmi_features(unsigned long index, unsigned long *out)
>   	return args.a0;
>   }
>   
> +/**
> + * 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 int rmi_rmm_config_set(unsigned long cfg_ptr)
> +{
> +	struct arm_smccc_1_2_regs regs = {
> +		SMC_RMI_RMM_CONFIG_SET, cfg_ptr,
> +	};
> +
> +	rmi_smccc_invoke(&regs);
> +
> +	return regs.a0;
> +}
> +

The comments for rmi_rmm_config_set() can be dropped since its logic is simply enough and
the code is self-explainning. Besides, I would move this right before its only caller
rmi_configure().

I would suggest drop this function by combining its logics into the only caller
rmi_configure(), seeing below for more details.

>   unsigned long rmi_feat_reg(unsigned long index)
>   {
>   	if (WARN_ON(index >= RMI_FEAT_REG_COUNT))
> @@ -98,6 +117,62 @@ 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) {
> +		pr_err("Unable to allocate memory for RMM config\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 (%d)\n", ret);
> +		ret = -EINVAL;
> +	}
> +

I would suggest to drop rmi_rmm_config_set() by combining its logic to rmi_configure().

	struct arm_smccc_1_2_regs args = { SMC_RMI_RMM_CONFIG_SET };

	args.a1 = virt_to_phys(config);
	rmi_smccc_invoke(&args);
	if (args.a0 != RMI_SUCCESS) {
		pr_err("RMM config set failed (%ld)\n", args.a0);
		ret = -EINVAL;
	}
	

> +	free_page((unsigned long)config);
> +	return ret;
> +}
> +
>   static int __init arm64_init_rmi(void)
>   {
>   	int ret;
> @@ -111,6 +186,10 @@ static int __init arm64_init_rmi(void)
>   	if (ret)
>   		return ret;
>   
> +	ret = rmi_configure();
> +	if (ret)
> +		return ret;
> +
>   	return 0;
>   }
>   

Thanks,
Gavin