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