Re: [PATCH v2 1/3] arm/mpu: Implement setup_mm for MPU systems

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 11/11/2025 11:15, Harry Ramsey wrote:
> Implement `setup_mm` for MPU systems. This variant does not require
> setting up a direct map.
> 
> To reduce code duplication the common initalisation code for both MPU
> and MMU Arm64 configurations is refactored into `setup_mm`. Platform-specific
> setup steps are now handled by a new helper function `setup_mm_helper`.
> 
> Signed-off-by: Harry Ramsey <harry.ramsey@xxxxxxx>
> ---
> Changes in v2:
> - Improve clarity with regards to MPU setup in setup_mm
> ---
>  xen/arch/arm/arm64/mmu/mm.c   | 26 +------------------
>  xen/arch/arm/include/asm/mm.h |  2 ++
>  xen/arch/arm/mm.c             | 48 +++++++++++++++++++++++++++++++++++
>  xen/arch/arm/mpu/mm.c         | 30 ++++++++++++++++++++--
>  4 files changed, 79 insertions(+), 27 deletions(-)
> 
> diff --git a/xen/arch/arm/arm64/mmu/mm.c b/xen/arch/arm/arm64/mmu/mm.c
> index 3e64be6ae6..70b53be032 100644
> --- a/xen/arch/arm/arm64/mmu/mm.c
> +++ b/xen/arch/arm/arm64/mmu/mm.c
> @@ -4,8 +4,6 @@
>  #include <xen/llc-coloring.h>
>  #include <xen/mm.h>
>  #include <xen/pfn.h>
> -#include <xen/static-memory.h>
> -#include <xen/static-shmem.h>
> 
>  #include <asm/setup.h>
> 
> @@ -240,33 +238,18 @@ static void __init setup_directmap_mappings(unsigned 
> long base_mfn,
>          panic("Unable to setup the directmap mappings.\n");
>  }
> 
> -void __init setup_mm(void)
> +void __init setup_mm_helper(void)
>  {
>      const struct membanks *banks = bootinfo_get_mem();
>      paddr_t ram_start = INVALID_PADDR;
>      paddr_t ram_end = 0;
> -    paddr_t ram_size = 0;
>      unsigned int i;
> 
> -    init_pdx();
> -
> -    /*
> -     * We need some memory to allocate the page-tables used for the directmap
> -     * mappings. But some regions may contain memory already allocated
> -     * for other uses (e.g. modules, reserved-memory...).
> -     *
> -     * For simplicity, add all the free regions in the boot allocator.
> -     */
> -    populate_boot_allocator();
> -
> -    total_pages = 0;
> -
>      for ( i = 0; i < banks->nr_banks; i++ )
>      {
>          const struct membank *bank = &banks->bank[i];
>          paddr_t bank_end = bank->start + bank->size;
> 
> -        ram_size = ram_size + bank->size;
>          ram_start = min(ram_start, bank->start);
>          ram_end = max(ram_end, bank_end);
> 
> @@ -274,16 +257,9 @@ void __init setup_mm(void)
>                                   PFN_DOWN(bank->size));
>      }
> 
> -    total_pages += ram_size >> PAGE_SHIFT;
> -
>      directmap_virt_end = XENHEAP_VIRT_START + ram_end - ram_start;
>      directmap_mfn_start = maddr_to_mfn(ram_start);
>      directmap_mfn_end = maddr_to_mfn(ram_end);
> -
> -    setup_frametable_mappings(ram_start, ram_end);
> -
> -    init_staticmem_pages();
> -    init_sharedmem_pages();
>  }
> 
>  /*
> diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
> index 7a93dad2ed..f702f4a0d6 100644
> --- a/xen/arch/arm/include/asm/mm.h
> +++ b/xen/arch/arm/include/asm/mm.h
> @@ -202,6 +202,8 @@ extern void remove_early_mappings(void);
>  extern int prepare_secondary_mm(int cpu);
>  /* Map a frame table to cover physical addresses ps through pe */
>  extern void setup_frametable_mappings(paddr_t ps, paddr_t pe);
> +/* Helper function to setup memory management */
> +void setup_mm_helper(void);
>  /* map a physical range in virtual memory */
>  void __iomem *ioremap_attr(paddr_t start, size_t len, unsigned int 
> attributes);
> 
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 3b05b46ee0..c1208de26c 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -12,8 +12,12 @@
>  #include <xen/grant_table.h>
>  #include <xen/guest_access.h>
>  #include <xen/mm.h>
> +#include <xen/static-memory.h>
> +#include <xen/static-shmem.h>
>  #include <xen/vmap.h>
> 
> +#include <asm/setup.h>
> +
>  #include <xsm/xsm.h>
> 
>  #include <public/memory.h>
> @@ -24,6 +28,50 @@
> 
>  unsigned long frametable_base_pdx __read_mostly;
> 
> +#if defined(CONFIG_ARM_64) || defined(CONFIG_MPU)
> +void __init setup_mm(void)
> +{
> +    const struct membanks *banks = bootinfo_get_mem();
> +    paddr_t ram_start = INVALID_PADDR;
> +    paddr_t ram_end = 0;
> +    paddr_t ram_size = 0;
> +    unsigned int i;
> +
> +    init_pdx();
> +
> +    for ( i = 0; i < banks->nr_banks; i++ )
> +    {
> +        const struct membank *bank = &banks->bank[i];
> +        paddr_t bank_end = bank->start + bank->size;
> +
> +        ram_size = ram_size + bank->size;
> +        ram_start = min(ram_start, bank->start);
> +        ram_end = max(ram_end, bank_end);
> +    }
> +
> +    total_pages = ram_size >> PAGE_SHIFT;
> +
> +    /*
> +     * On MMU systems we need some memory to allocate the page-tables used 
> for
> +     * the directmap mappings.  But some regions may contain memory already
> +     * allocated for other uses (e.g. modules, reserved-memory...).
> +     *
> +     * On MPU systems we need to pre-reserve regions that were allocated for
> +     * other uses (e.g. modules, reserved-memory...).
I'm not sure I understand this part of the comment with regards to
populate_boot_allocator(). Could you please explain?

~Michal