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@arm.com>
---
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...).
+     *
+     * For simplicity, add all the free regions in the boot allocator.
+     */
+    populate_boot_allocator();
+
+    setup_mm_helper();
+
+    setup_frametable_mappings(ram_start, ram_end);
+
+    init_staticmem_pages();
+    init_sharedmem_pages();
+}
+#endif
+
 bool flags_has_rwx(unsigned int flags)
 {
     /*
diff --git a/xen/arch/arm/mpu/mm.c b/xen/arch/arm/mpu/mm.c
index 3f155b7db2..b80edcf1ca 100644
--- a/xen/arch/arm/mpu/mm.c
+++ b/xen/arch/arm/mpu/mm.c
@@ -5,12 +5,14 @@
 #include <xen/init.h>
 #include <xen/lib.h>
 #include <xen/mm.h>
+#include <xen/pfn.h>
 #include <xen/sizes.h>
 #include <xen/spinlock.h>
 #include <xen/types.h>
 #include <asm/mpu.h>
 #include <asm/mpu/mm.h>
 #include <asm/page.h>
+#include <asm/setup.h>
 #include <asm/sysregs.h>

 struct page_info *frame_table;
@@ -378,9 +380,33 @@ int map_pages_to_xen(unsigned long virt, mfn_t mfn, unsigned long nr_mfns,
     return xen_mpumap_update(virt, mfn_to_maddr(mfn_add(mfn, nr_mfns)), flags);
 }

-void __init setup_mm(void)
+/*
+ * Heap must be statically configured in Device Tree through "xen,static-heap"
+ * on MPU systems, use setup_mm_helper() for that.
+ */
+void __init setup_mm_helper(void)
 {
-    BUG_ON("unimplemented");
+    const struct membanks *reserved_mem = bootinfo_get_reserved_mem();
+    unsigned int bank = 0;
+
+    for ( ; bank < reserved_mem->nr_banks; bank++ )
+    {
+        if ( reserved_mem->bank[bank].type == MEMBANK_STATIC_HEAP )
+        {
+            paddr_t bank_start = round_pgup(reserved_mem->bank[bank].start);
+            paddr_t bank_size = round_pgdown(reserved_mem->bank[bank].size);
+            paddr_t bank_end = bank_start + bank_size;
+
+            /* Map static heap with one MPU protection region */
+            if ( xen_mpumap_update(bank_start, bank_end, PAGE_HYPERVISOR) )
+                panic("Failed to map static heap\n");
+
+            break;
+        }
+    }
+
+    if ( bank == reserved_mem->nr_banks )
+        panic("No static heap memory bank found\n");
 }

 int modify_xen_mappings(unsigned long s, unsigned long e, unsigned int nf)
--
2.43.0

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@arm.com>
> ---
> 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

On 12/11/2025 12:40, Orzel, Michal wrote:
>
> 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@arm.com>
>> ---
>> 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?
I think I should remove the MPU section and move this comment into patch 
3 as it is confusing without the additional context of reference counting.

During Xen initialization, the MPU assigns a refcount of 1 to 
pre-allocated regions in head.S prepare_xen_region. Unlike an MMU, an 
MPU has no virtual memory, so we must prevent these regions from being 
freed or remapped to non-preallocated areas.

>
> ~Michal
>
~Harry

Hi Michal,

>>> +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?

Maybe here we should just write that on MPU system we are populating the boot allocator with the
static heap region, since static heap is mandatory for MPU.

What do you think?

e.g.

/*
 * On MMU system…
 * […]
 * 
 * On MPU system we need to populate the boot allocator with the static heap region, on such systems
 * the static heap feature is mandatory.
 *

Cheers,
Luca

On 12/11/2025 17:06, Luca Fancellu wrote:
> Hi Michal,
> 
>>>> +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?
> 
> Maybe here we should just write that on MPU system we are populating the boot allocator with the
> static heap region, since static heap is mandatory for MPU.
> 
> What do you think?
The reason for the original comment was to explain why we need to call
populate_boot_allocator() that early (i.e. before setting up direct map and not
before setting up frametable). It's not about explaining why we need to populate
boot allocator because that is rather clear. In case of MPU I don't think there
is a reason for doing that early, so we might not need any reasoning.

~Michal

HI Michal,

> On 17 Nov 2025, at 12:51, Orzel, Michal <Michal.Orzel@amd.com> wrote:
> 
> 
> 
> On 12/11/2025 17:06, Luca Fancellu wrote:
>> Hi Michal,
>> 
>>>>> +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?
>> 
>> Maybe here we should just write that on MPU system we are populating the boot allocator with the
>> static heap region, since static heap is mandatory for MPU.
>> 
>> What do you think?
> The reason for the original comment was to explain why we need to call
> populate_boot_allocator() that early (i.e. before setting up direct map and not
> before setting up frametable). It's not about explaining why we need to populate
> boot allocator because that is rather clear. In case of MPU I don't think there
> is a reason for doing that early, so we might not need any reasoning.

ok sounds good, we can avoid mentioning the MPU section all together.

Cheers,
Luca