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Message-ID: <aVpWpLV4Dut5Muo2@kernel.org>
Date: Sun, 4 Jan 2026 14:01:40 +0200
From: Mike Rapoport <rppt@...nel.org>
To: Klara Modin <klarasmodin@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Alex Shi <alexs@...nel.org>, Alexander Gordeev <agordeev@...ux.ibm.com>,
Andreas Larsson <andreas@...sler.com>,
Borislav Petkov <bp@...en8.de>, Brian Cain <bcain@...nel.org>,
"Christophe Leroy (CS GROUP)" <chleroy@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
"David S. Miller" <davem@...emloft.net>,
Dave Hansen <dave.hansen@...ux.intel.com>,
David Hildenbrand <david@...nel.org>,
Dinh Nguyen <dinguyen@...nel.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Guo Ren <guoren@...nel.org>, Heiko Carstens <hca@...ux.ibm.com>,
Helge Deller <deller@....de>, Huacai Chen <chenhuacai@...nel.org>,
Ingo Molnar <mingo@...hat.com>,
Johannes Berg <johannes@...solutions.net>,
John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
Jonathan Corbet <corbet@....net>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
Magnus Lindholm <linmag7@...il.com>,
Matt Turner <mattst88@...il.com>, Max Filippov <jcmvbkbc@...il.com>,
Michael Ellerman <mpe@...erman.id.au>,
Michal Hocko <mhocko@...e.com>, Michal Simek <monstr@...str.eu>,
Muchun Song <muchun.song@...ux.dev>,
Oscar Salvador <osalvador@...e.de>,
Palmer Dabbelt <palmer@...belt.com>,
Pratyush Yadav <pratyush@...nel.org>,
Richard Weinberger <richard@....at>,
Russell King <linux@...linux.org.uk>,
Stafford Horne <shorne@...il.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
Thomas Gleixner <tglx@...utronix.de>,
Vasily Gorbik <gor@...ux.ibm.com>, Vineet Gupta <vgupta@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>,
x86@...nel.org, linux-alpha@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-csky@...r.kernel.org,
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sparclinux@...r.kernel.org
Subject: [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)
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@...il.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@...il.com>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.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);
}
/*
--
2.51.0
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