[PATCH 3.5] arm: make initialization of zero page independent of the memory map (was Re: [PATCH v2 22/28] arch, mm: consolidate initialization of nodes, zones and memory map)

Mike Rapoport
2026-01-04T12:02:08Z

Andrew,

Can you please stick this between patch 3 (arm: introduce
arch_zone_limits_init()) and patch 4 (arm64: introduce
arch_zone_limits_init())?

From 35d016bbf5da7c08cc5c5547c85558fc50cb63aa Mon Sep 17 00:00:00 2001
From: Klara Modin <klarasmodin@gmail.com>
Date: Sat, 3 Jan 2026 20:40:09 +0200
Subject: [PATCH] arm: make initialization of zero page independent of the
memory map

Unlike most architectures, arm keeps a struct page pointer to the
empty_zero_page and to initialize it requires conversion of a virtual
address to page which makes it necessary to have memory map initialized
before creating the empty_zero_page.

Make empty_zero_page a stataic array in BSS to decouple it's
initialization from the initialization of the memory map.

This also aligns arm with vast majorty of architectures.

Signed-off-by: Klara Modin <klarasmodin@gmail.com>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
arch/arm/include/asm/pgtable.h | 4 ++--
arch/arm/mm/mmu.c | 10 +---------
arch/arm/mm/nommu.c | 10 +---------
3 files changed, 4 insertions(+), 20 deletions(-)

diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index 86378eec7757..6fa9acd6a7f5 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -15,8 +15,8 @@
* ZERO_PAGE is a global shared page that is always zero: used
* for zero-mapped memory areas etc..
*/
-extern struct page *empty_zero_page;
-#define ZERO_PAGE(vaddr) (empty_zero_page)
+extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
+#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
#endif

#include <asm-generic/pgtable-nopud.h>
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 8bac96e205ac..518def8314e7 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -45,7 +45,7 @@ extern unsigned long __atags_pointer;
* empty_zero_page is a special page that is used for
* zero-initialized data and COW.
*/
-struct page *empty_zero_page;
+unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
EXPORT_SYMBOL(empty_zero_page);

/*
@@ -1754,8 +1754,6 @@ static void __init early_fixmap_shutdown(void)
*/
void __init paging_init(const struct machine_desc *mdesc)
{
- void *zero_page;
-
#ifdef CONFIG_XIP_KERNEL
/* Store the kernel RW RAM region start/end in these variables */
kernel_sec_start = CONFIG_PHYS_OFFSET & SECTION_MASK;
@@ -1781,13 +1779,7 @@ void __init paging_init(const struct machine_desc *mdesc)

top_pmd = pmd_off_k(0xffff0000);

- /* allocate the zero page. */
- zero_page = early_alloc(PAGE_SIZE);
-
bootmem_init();
-
- empty_zero_page = virt_to_page(zero_page);
- __flush_dcache_folio(NULL, page_folio(empty_zero_page));
}

void __init early_mm_init(const struct machine_desc *mdesc)
diff --git a/arch/arm/mm/nommu.c b/arch/arm/mm/nommu.c
index d638cc87807e..7e42d8accec6 100644
--- a/arch/arm/mm/nommu.c
+++ b/arch/arm/mm/nommu.c
@@ -31,7 +31,7 @@ unsigned long vectors_base;
* empty_zero_page is a special page that is used for
* zero-initialized data and COW.
*/
-struct page *empty_zero_page;
+unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
EXPORT_SYMBOL(empty_zero_page);

#ifdef CONFIG_ARM_MPU
@@ -156,18 +156,10 @@ void __init adjust_lowmem_bounds(void)
*/
void __init paging_init(const struct machine_desc *mdesc)
{
- void *zero_page;
-
early_trap_init((void *)vectors_base);
mpu_setup();

- /* allocate the zero page. */
- zero_page = (void *)memblock_alloc_or_panic(PAGE_SIZE, PAGE_SIZE);
-
bootmem_init();
-
- empty_zero_page = virt_to_page(zero_page);
- flush_dcache_page(empty_zero_page);
}

/*