Re: [PATCH 1/5] xen/arm: mpu: Ensure that the page size is 4KB (arm32)

[Julien Grall <julien@xxxxxxx>]

Hi Ayan,

On 04/02/2025 19:23, Ayan Kumar Halder wrote:
> Similar to "xen/arm: mpu: Define Xen start address for MPU systems", added
Can you provide the commit ID? Also, we tend to use present for 
describing changes, so s/added/add/
> a build assertion to ensure that the page size is 4KB.
>
> Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
> ---
>   xen/arch/arm/arm32/Makefile     |  1 +
>   xen/arch/arm/arm32/mpu/Makefile |  1 +
>   xen/arch/arm/arm32/mpu/mm.c     | 15 +++++++++++++++
>   3 files changed, 17 insertions(+)
>   create mode 100644 xen/arch/arm/arm32/mpu/Makefile
>   create mode 100644 xen/arch/arm/arm32/mpu/mm.c
>
> diff --git a/xen/arch/arm/arm32/Makefile b/xen/arch/arm/arm32/Makefile
> index 40a2b4803f..537969d753 100644
> --- a/xen/arch/arm/arm32/Makefile
> +++ b/xen/arch/arm/arm32/Makefile
> @@ -1,5 +1,6 @@
>   obj-y += lib/
>   obj-$(CONFIG_MMU) += mmu/
> +obj-$(CONFIG_MPU) += mpu/
>   
>   obj-$(CONFIG_EARLY_PRINTK) += debug.o
>   obj-y += domctl.o
> diff --git a/xen/arch/arm/arm32/mpu/Makefile b/xen/arch/arm/arm32/mpu/Makefile
> new file mode 100644
> index 0000000000..b18cec4836
> --- /dev/null
> +++ b/xen/arch/arm/arm32/mpu/Makefile
> @@ -0,0 +1 @@
> +obj-y += mm.o
> diff --git a/xen/arch/arm/arm32/mpu/mm.c b/xen/arch/arm/arm32/mpu/mm.c
> new file mode 100644
> index 0000000000..0b8748e575
> --- /dev/null
> +++ b/xen/arch/arm/arm32/mpu/mm.c
> @@ -0,0 +1,15 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#include <xen/lib.h>
> +#include <xen/init.h>
> +#include <xen/sizes.h>
> +
> +static void __init __maybe_unused build_assertions(void)
> +{
> +    /*
> +     * Unlike MMU, MPU does not use pages for translation. However, we continue
> +     * to use PAGE_SIZE to denote 4KB. This is so that the existing memory
> +     * management based on pages, continue to work for now.
> +     */
> +    BUILD_BUG_ON(PAGE_SIZE != SZ_4K);
> +}
I think it would be better if we create an arm/mpu/mm.c which would 
contain any common code/requirements between arm64 and arm32 (I assume 
there will be quire a few).
Cheers,

--
Julien Grall