Re: [PATCH v1 1/4] xen/arm: mpu: Introduce choice between MMU and MPU

[Julien Grall <julien@xxxxxxx>]

Hi,

On 23/08/2024 17:31, Ayan Kumar Halder wrote:
> There are features in the forthcoming patches which are dependent on
> MPU. For eg fixed start address.
> Also, some of the Xen features (eg STATIC_MEMORY) will be selected
> by the MPU configuration.
>
> Thus, this patch introduces a choice between MMU and MPU for the type
> of memory management system. By default, MMU is selected.
> All the current platforms are now made dependent on MMU.
>
> Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
> ---
>   xen/arch/arm/Kconfig           | 17 ++++++++++++++++-
>   xen/arch/arm/platforms/Kconfig |  2 +-
>   2 files changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/xen/arch/arm/Kconfig b/xen/arch/arm/Kconfig
> index 323c967361..686948cefd 100644
> --- a/xen/arch/arm/Kconfig
> +++ b/xen/arch/arm/Kconfig
> @@ -58,10 +58,25 @@ config PADDR_BITS
>         default 40 if ARM_PA_BITS_40
>         default 48 if ARM_64
>   
> +choice
> +       prompt "Memory management system"
> +       default MMU if ARM
> +       help
> +         User can choose between the different forms of memory management 
> system.
> +         Most of the Arm based systems support MMU.
I feel this is quite subjective. So I would drop it.

> +
>   config MMU
> -       def_bool y
> +       bool "MMU"
>         select HAS_PMAP
>         select HAS_VMAP
> +       help
> +         Memory management unit is supported on most Arm based systems.
For this case, I would write "Select it you are plan to run Xen on 
Armv7-A or Armv8-A".

> +
> +config MPU
> +       bool "MPU"
I think it should be gated by UNSUPPORTED. SUPPORT.md also needs to be 
updated.
> +       help
> +         Memory protection unit is supported on some Cortex-R systems.
Why do you make this specific to Cortex-R? Shouldn't this instead be 
Armv8-R?
> +endchoice
>   
>   source "arch/Kconfig"
>   
> diff --git a/xen/arch/arm/platforms/Kconfig b/xen/arch/arm/platforms/Kconfig
> index 76f7e76b1b..02322c259c 100644
> --- a/xen/arch/arm/platforms/Kconfig
> +++ b/xen/arch/arm/platforms/Kconfig
> @@ -1,5 +1,5 @@
>   choice
> -       prompt "Platform Support"
> +       prompt "Platform Support" if MMU
>         default ALL_PLAT
>         help
>         Choose which hardware platform to enable in Xen.
--
Julien Grall