Re: [PATCH v14 07/44] arm64: RMI: Configure the RMM with the host's page size

[Gavin Shan]

Hi Steven,

On 5/13/26 11:17 PM, Steven Price wrote:
> 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 granulatity
> equal to PAGE_SIZE.
>
> Signed-off-by: Steven Price <steven.price@xxxxxxx>
> ---
> Changes since v13:
>   * Moved out of KVM.
> ---
>   arch/arm64/kernel/rmi.c | 42 +++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 42 insertions(+)
>
> diff --git a/arch/arm64/kernel/rmi.c b/arch/arm64/kernel/rmi.c
> index 99c1ccc35c11..a14ead5dedda 100644
> --- a/arch/arm64/kernel/rmi.c
> +++ b/arch/arm64/kernel/rmi.c
> @@ -49,6 +49,45 @@ static int rmi_check_version(void)
>   	return 0;
>   }
>   
> +static int rmi_configure(void)
> +{
> +	struct rmm_config *config __free(free_page) = NULL;
> +	unsigned long ret;
> +
> +	config = (struct rmm_config *)get_zeroed_page(GFP_KERNEL);
> +	if (!config)
> +		return -ENOMEM;
> +
> +	switch (PAGE_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:
> +		pr_err("Unsupported PAGE_SIZE for RMM\n");
> +		return -EINVAL;
> +	}
> +
> +	ret = rmi_rmm_config_set(virt_to_phys(config));
> +	if (ret) {
> +		pr_err("RMM config set failed\n");
> +		return -EINVAL;
> +	}
> +

Looking at branch 'topics/rmm-v2.0-poc_2' of RMM implementation, the granule size
is fixed to be 4KB at present. I'm not sure if I have looked into correct RMM
implementation, but 'topics/rmm-v2.0-poc_2' is recommended one in the cover
letter.

Besides, there has checks in the handler of the RMI command to make sure that
struct rmm_config::tracking_region_size to be 1GB, indicated by zero. It maybe
worthy to set it before call to rmi_rmm_config_set().

	config.tracking_region_size = 0; /* 1GB */
	ret = rmi_rmm_config_set(virt_to_phys(config));


> +	ret = rmi_rmm_activate();
> +	if (ret) {
> +		pr_err("RMM activate failed\n");
> +		return -ENXIO;
> +	}
> +
> +	return 0;
> +}
> +
>   static int __init arm64_init_rmi(void)
>   {
>   	/* Continue without realm support if we can't agree on a version */
> @@ -60,6 +99,9 @@ static int __init arm64_init_rmi(void)
>   	if (WARN_ON(rmi_features(1, &rmm_feat_reg1)))
>   		return 0;
>   
> +	if (rmi_configure())
> +		return 0;
> +
>   	return 0;
>   }
>   subsys_initcall(arm64_init_rmi);

Thanks,
Gavin