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Miller" , Dave Hansen , David Hildenbrand , Dinh Nguyen , Geert Uytterhoeven , Guo Ren , Heiko Carstens , Helge Deller , Huacai Chen , Ingo Molnar , Johannes Berg , John Paul Adrian Glaubitz , Jonathan Corbet , Klara Modin , "Liam R. Howlett" , Lorenzo Stoakes , Magnus Lindholm , Matt Turner , Max Filippov , Michael Ellerman , Michal Hocko , Michal Simek , Mike Rapoport , Muchun Song , Oscar Salvador , Palmer Dabbelt , Pratyush Yadav , Richard Weinberger , Ritesh Harjani , Russell King , Stafford Horne , Suren Baghdasaryan , Thomas Bogendoerfer , Thomas Gleixner , Vasily Gorbik , Vineet Gupta , Vlastimil Babka , Will Deacon , x86@kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org, linux-cxl@vger.kernel.org, linux-doc@vger.kernel.org, linux-hexagon@vger.kernel.org, linux-kernel@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-openrisc@vger.kernel.org, linux-parisc@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-um@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev, sparclinux@vger.kernel.org Subject: [PATCH v3 04/29] arm: make initialization of zero page independent of the memory map Date: Sun, 11 Jan 2026 10:20:38 +0200 Message-ID: <20260111082105.290734-5-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260111082105.290734-1-rppt@kernel.org> References: <20260111082105.290734-1-rppt@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 2C08280013 X-Stat-Signature: 89hhi7chygophkraja48tai6ga96k46t X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1768119745-516762 X-HE-Meta: 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 R2OiXncO 3kQ+TkOLy7yggYLgicGRCS6xypmHn4kuakLXo8DouRdiYvo3E/h47v519kW2S4zY/ObbJYXQQES9c2PMALN23rmYXOf7ueNO02hiChSC0kK8MMbTSm4sj4AVmLYT/ef6IFdRpUJYIa6sZ0If87CVgC3FxuSlwH2vRefxLLI/tnZjVU7hOju3t+OFLDkPe3PjGdqM/QNszcQquUmZYIh7+LbtWZyMd8r8v1O5FY6I0seuowb172Dy6fRcc2AQRGT3KblDJS0bBh5IMWYLb2SwJJUwNDfuL8XQHEccDPpHaRopYOXupMhPPs6CByAGUlV0lQjzsm4stl+7ZNYc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Klara Modin 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 Signed-off-by: Mike Rapoport (Microsoft) --- 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 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