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

[Suzuki K Poulose]

On 08/09/2026 08:04, Gavin Shan wrote:
> Hi Suzuki,
> 
> On 9/7/26 7:59 PM, Suzuki K Poulose wrote:
>> From: Steven Price <steven.price at 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 at arm.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose at 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;
>      }
> 

I can add that, doesn't hurt.

>> +
>> +    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;
>      }
> 

Ack

>> 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().

Ack

Thank you for the review

Cheers
Suzuki