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Subject[PATCH v2 2/2] ARM: mm: convert empty_zero_page to array for consistency
Date
ARM architecture is the only one to have empty_zero_page to be a
struct page pointer, while in all other implementations empty_zero_page is
a data pointer or directly an array(the zero page itself). So let's convert
empty_zero_page to an array for consistency and to avoid an early
allocation+dcache flush. Being the array in .bss it will be cleared earlier
in a more linear way(and a bit faster) way.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
---
V1->V2:
* create patch suggested by Arnd Bergmann
---
arch/arm/include/asm/pgtable.h | 4 ++--
arch/arm/mm/mmu.c | 10 +---------
arch/arm/mm/nommu.c | 14 +-------------
3 files changed, 4 insertions(+), 24 deletions(-)

diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index ef48a55e9af8..de402b345f55 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[];
+#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
#endif

#ifndef CONFIG_MMU
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 463fc2a8448f..f05a5471a45a 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);

/*
@@ -1760,8 +1760,6 @@ static void __init early_fixmap_shutdown(void)
*/
void __init paging_init(const struct machine_desc *mdesc)
{
- void *zero_page;
-
pr_debug("physical kernel sections: 0x%08llx-0x%08llx\n",
kernel_sec_start, kernel_sec_end);

@@ -1782,13 +1780,7 @@ 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_page(NULL, 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 c1494a4dee25..e0c3f59d1c5a 100644
--- a/arch/arm/mm/nommu.c
+++ b/arch/arm/mm/nommu.c
@@ -30,7 +30,7 @@ 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
@@ -155,21 +155,9 @@ 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 = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
- if (!zero_page)
- panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
- __func__, PAGE_SIZE, PAGE_SIZE);
-
bootmem_init();
-
- empty_zero_page = virt_to_page(zero_page);
- flush_dcache_page(empty_zero_page);
}

/*
--
2.34.1
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