[PATCH 12/13] arch, mm: introduce arch_mm_preinit

From: Mike Rapoport
Date: Thu Mar 06 2025 - 13:55:39 EST

From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>

Currently, implementation of mem_init() in every architecture consists of
one or more of the following:

* initializations that must run before page allocator is active, for
instance swiotlb_init()
* a call to memblock_free_all() to release all the memory to the buddy
allocator
* initializations that must run after page allocator is ready and there is
no arch-specific hook other than mem_init() for that, like for example
register_page_bootmem_info() in x86 and sparc64 or simple setting of
mem_init_done = 1 in several architectures
* a bunch of semi-related stuff that apparently had no better place to
live, for example a ton of BUILD_BUG_ON()s in parisc.

Introduce arch_mm_preinit() that will be the first thing called from
mm_core_init(). On architectures that have initializations that must happen
before the page allocator is ready, move those into arch_mm_preinit() along
with the code that does not depend on ordering with page allocator setup.

On several architectures this results in reduction of mem_init() to a
single call to memblock_free_all() that allows its consolidation next.

Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
---
arch/arc/mm/init.c | 13 ++++++-------
arch/arm/mm/init.c | 21 ++++++++++++---------
arch/arm64/mm/init.c | 21 ++++++++++++---------
arch/mips/mm/init.c | 11 +++++++----
arch/powerpc/mm/mem.c | 9 ++++++---
arch/riscv/mm/init.c | 8 ++++++--
arch/s390/mm/init.c | 5 ++++-
arch/sparc/mm/init_32.c | 5 ++++-
arch/um/kernel/mem.c | 7 +++++--
arch/x86/mm/init_32.c | 6 +++++-
arch/x86/mm/init_64.c | 5 ++++-
include/linux/mm.h | 1 +
mm/mm_init.c | 5 +++++
13 files changed, 77 insertions(+), 40 deletions(-)

diff --git a/arch/arc/mm/init.c b/arch/arc/mm/init.c
index 11ce638731c9..90715b4a0bfa 100644
--- a/arch/arc/mm/init.c
+++ b/arch/arc/mm/init.c
@@ -157,11 +157,16 @@ void __init setup_arch_memory(void)
free_area_init(max_zone_pfn);
}

-static void __init highmem_init(void)
+void __init arch_mm_preinit(void)
{
#ifdef CONFIG_HIGHMEM
memblock_phys_free(high_mem_start, high_mem_sz);
#endif
+
+ BUILD_BUG_ON((PTRS_PER_PGD * sizeof(pgd_t)) > PAGE_SIZE);
+ BUILD_BUG_ON((PTRS_PER_PUD * sizeof(pud_t)) > PAGE_SIZE);
+ BUILD_BUG_ON((PTRS_PER_PMD * sizeof(pmd_t)) > PAGE_SIZE);
+ BUILD_BUG_ON((PTRS_PER_PTE * sizeof(pte_t)) > PAGE_SIZE);
}

/*
@@ -172,13 +177,7 @@ static void __init highmem_init(void)
*/
void __init mem_init(void)
{
- highmem_init();
memblock_free_all();
-
- BUILD_BUG_ON((PTRS_PER_PGD * sizeof(pgd_t)) > PAGE_SIZE);
- BUILD_BUG_ON((PTRS_PER_PUD * sizeof(pud_t)) > PAGE_SIZE);
- BUILD_BUG_ON((PTRS_PER_PMD * sizeof(pmd_t)) > PAGE_SIZE);
- BUILD_BUG_ON((PTRS_PER_PTE * sizeof(pte_t)) > PAGE_SIZE);
}

#ifdef CONFIG_HIGHMEM
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 7bb5ce02b9b5..7222100b0631 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -237,12 +237,7 @@ static inline void poison_init_mem(void *s, size_t count)
*p++ = 0xe7fddef0;
}

-/*
- * mem_init() marks the free areas in the mem_map and tells us how much
- * memory is free. This is done after various parts of the system have
- * claimed their memory after the kernel image.
- */
-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
#ifdef CONFIG_ARM_LPAE
swiotlb_init(max_pfn > arm_dma_pfn_limit, SWIOTLB_VERBOSE);
@@ -253,9 +248,6 @@ void __init mem_init(void)
memblock_phys_free(PHYS_OFFSET, __pa(swapper_pg_dir) - PHYS_OFFSET);
#endif

- /* this will put all unused low memory onto the freelists */
- memblock_free_all();
-
/*
* Check boundaries twice: Some fundamental inconsistencies can
* be detected at build time already.
@@ -271,6 +263,17 @@ void __init mem_init(void)
#endif
}

+/*
+ * mem_init() marks the free areas in the mem_map and tells us how much
+ * memory is free. This is done after various parts of the system have
+ * claimed their memory after the kernel image.
+ */
+void __init mem_init(void)
+{
+ /* this will put all unused low memory onto the freelists */
+ memblock_free_all();
+}
+
#ifdef CONFIG_STRICT_KERNEL_RWX
struct section_perm {
const char *name;
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index a48fcccd67fa..8eff6a6eb11e 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -362,12 +362,7 @@ void __init bootmem_init(void)
memblock_dump_all();
}

-/*
- * mem_init() marks the free areas in the mem_map and tells us how much memory
- * is free. This is done after various parts of the system have claimed their
- * memory after the kernel image.
- */
-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
unsigned int flags = SWIOTLB_VERBOSE;
bool swiotlb = max_pfn > PFN_DOWN(arm64_dma_phys_limit);
@@ -391,9 +386,6 @@ void __init mem_init(void)
swiotlb_init(swiotlb, flags);
swiotlb_update_mem_attributes();

- /* this will put all unused low memory onto the freelists */
- memblock_free_all();
-
/*
* Check boundaries twice: Some fundamental inconsistencies can be
* detected at build time already.
@@ -419,6 +411,17 @@ void __init mem_init(void)
}
}

+/*
+ * mem_init() marks the free areas in the mem_map and tells us how much memory
+ * is free. This is done after various parts of the system have claimed their
+ * memory after the kernel image.
+ */
+void __init mem_init(void)
+{
+ /* this will put all unused low memory onto the freelists */
+ memblock_free_all();
+}
+
void free_initmem(void)
{
void *lm_init_begin = lm_alias(__init_begin);
diff --git a/arch/mips/mm/init.c b/arch/mips/mm/init.c
index e7882874ba2f..619e2e394392 100644
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -427,7 +427,7 @@ void __init paging_init(void)
static struct kcore_list kcore_kseg0;
#endif

-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
/*
* When PFN_PTE_SHIFT is greater than PAGE_SHIFT we won't have enough PTE
@@ -437,7 +437,6 @@ void __init mem_init(void)

maar_init();
setup_zero_pages(); /* Setup zeroed pages. */
- memblock_free_all();

#ifdef CONFIG_64BIT
if ((unsigned long) &_text > (unsigned long) CKSEG0)
@@ -448,13 +447,17 @@ void __init mem_init(void)
#endif
}
#else /* CONFIG_NUMA */
-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
setup_zero_pages(); /* This comes from node 0 */
- memblock_free_all();
}
#endif /* !CONFIG_NUMA */

+void __init mem_init(void)
+{
+ memblock_free_all();
+}
+
void free_init_pages(const char *what, unsigned long begin, unsigned long end)
{
unsigned long pfn;
diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index 1bc94bca9944..68efdaf14e58 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -273,7 +273,7 @@ void __init paging_init(void)
mark_nonram_nosave();
}

-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
/*
* book3s is limited to 16 page sizes due to encoding this in
@@ -295,8 +295,6 @@ void __init mem_init(void)

kasan_late_init();

- memblock_free_all();
-
#if defined(CONFIG_PPC_E500) && !defined(CONFIG_SMP)
/*
* If smp is enabled, next_tlbcam_idx is initialized in the cpu up
@@ -329,6 +327,11 @@ void __init mem_init(void)
#endif /* CONFIG_PPC32 */
}

+void __init mem_init(void)
+{
+ memblock_free_all();
+}
+
void free_initmem(void)
{
ppc_md.progress = ppc_printk_progress;
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index ac6d41e86243..9efadabf6be1 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -171,7 +171,7 @@ static void __init print_vm_layout(void)
static void print_vm_layout(void) { }
#endif /* CONFIG_DEBUG_VM */

-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
bool swiotlb = max_pfn > PFN_DOWN(dma32_phys_limit);
#ifdef CONFIG_FLATMEM
@@ -192,11 +192,15 @@ void __init mem_init(void)
}

swiotlb_init(swiotlb, SWIOTLB_VERBOSE);
- memblock_free_all();

print_vm_layout();
}

+void __init mem_init(void)
+{
+ memblock_free_all();
+}
+
/* Limit the memory size via mem. */
static phys_addr_t memory_limit;
#ifdef CONFIG_XIP_KERNEL
diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
index 08ebc9a9344a..6741b38fc864 100644
--- a/arch/s390/mm/init.c
+++ b/arch/s390/mm/init.c
@@ -156,7 +156,7 @@ static void pv_init(void)
swiotlb_update_mem_attributes();
}

-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
cpumask_set_cpu(0, &init_mm.context.cpu_attach_mask);
cpumask_set_cpu(0, mm_cpumask(&init_mm));
@@ -165,7 +165,10 @@ void __init mem_init(void)
kfence_split_mapping();

setup_zero_pages(); /* Setup zeroed pages. */
+}

+void __init mem_init(void)
+{
/* this will put all low memory onto the freelists */
memblock_free_all();
}
diff --git a/arch/sparc/mm/init_32.c b/arch/sparc/mm/init_32.c
index 043e9b6fadd0..e16c32c5728f 100644
--- a/arch/sparc/mm/init_32.c
+++ b/arch/sparc/mm/init_32.c
@@ -232,7 +232,7 @@ static void __init taint_real_pages(void)
}
}

-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
int i;

@@ -262,7 +262,10 @@ void __init mem_init(void)
memset(sparc_valid_addr_bitmap, 0, i << 2);

taint_real_pages();
+}

+void __init mem_init(void)
+{
memblock_free_all();
}

diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
index befed230aac2..cce387438e60 100644
--- a/arch/um/kernel/mem.c
+++ b/arch/um/kernel/mem.c
@@ -54,7 +54,7 @@ int kmalloc_ok = 0;
/* Used during early boot */
static unsigned long brk_end;

-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
/* clear the zero-page */
memset(empty_zero_page, 0, PAGE_SIZE);
@@ -66,10 +66,13 @@ void __init mem_init(void)
map_memory(brk_end, __pa(brk_end), uml_reserved - brk_end, 1, 1, 0);
memblock_free((void *)brk_end, uml_reserved - brk_end);
uml_reserved = brk_end;
+ max_pfn = max_low_pfn;
+}

+void __init mem_init(void)
+{
/* this will put all low memory onto the freelists */
memblock_free_all();
- max_pfn = max_low_pfn;
kmalloc_ok = 1;
}

diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 9ee8ec2bc5d1..16664c5464b5 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -691,13 +691,17 @@ static void __init test_wp_bit(void)
panic("Linux doesn't support CPUs with broken WP.");
}

-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
pci_iommu_alloc();

#ifdef CONFIG_FLATMEM
BUG_ON(!mem_map);
#endif
+}
+
+void __init mem_init(void)
+{
/* this will put all low memory onto the freelists */
memblock_free_all();

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 01ea7c6df303..f8981e29633c 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1348,10 +1348,13 @@ static void __init preallocate_vmalloc_pages(void)
panic("Failed to pre-allocate %s pages for vmalloc area\n", lvl);
}

-void __init mem_init(void)
+void __init arch_mm_preinit(void)
{
pci_iommu_alloc();
+}

+void __init mem_init(void)
+{
/* clear_bss() already clear the empty_zero_page */

/* this will put all memory onto the freelists */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 6fccd3b3248c..ae9cfb9612ea 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -42,6 +42,7 @@ struct folio_batch;

extern int sysctl_page_lock_unfairness;

+void arch_mm_preinit(void);
void mm_core_init(void);
void init_mm_internals(void);

diff --git a/mm/mm_init.c b/mm/mm_init.c
index 5e5f6ba73757..9cca3d497bf8 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -2668,11 +2668,16 @@ static void __init mem_init_print_info(void)
);
}

+void __init __weak arch_mm_preinit(void)
+{
+}
+
/*
* Set up kernel memory allocators
*/
void __init mm_core_init(void)
{
+ arch_mm_preinit();
/* Initializations relying on SMP setup */
BUILD_BUG_ON(MAX_ZONELISTS > 2);
build_all_zonelists(NULL);
--
2.47.2