[PATCH] arm: make initialization of zero page independent of the memory map

[Mike Rapoport (Microsoft)]

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 void * to decouple it's initialization from the
initialization of the memory map.

Signed-off-by: Mike Rapoport (Microsoft) <rppt at kernel.org>
---
 arch/arm/include/asm/pgtable.h |  4 ++--
 arch/arm/mm/mmu.c              | 10 +++-------
 arch/arm/mm/nommu.c            | 10 +++-------
 3 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index 86378eec7757..08bbd2aed6c9 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 void *empty_zero_page;
+#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..867258f1ae09 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;
+void *empty_zero_page;
 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;
@@ -1782,12 +1780,10 @@ 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);
+	empty_zero_page = early_alloc(PAGE_SIZE);
+	__cpuc_flush_dcache_area(empty_zero_page, 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..f80ff5a69fbb 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;
+void *empty_zero_page;
 EXPORT_SYMBOL(empty_zero_page);
 
 #ifdef CONFIG_ARM_MPU
@@ -156,18 +156,14 @@ 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);
+	empty_zero_page = memblock_alloc_or_panic(PAGE_SIZE, PAGE_SIZE);
+	__cpuc_flush_dcache_area(empty_zero_page, PAGE_SIZE);
 
 	bootmem_init();
-
-	empty_zero_page = virt_to_page(zero_page);
-	flush_dcache_page(empty_zero_page);
 }
 
 /*
-- 
2.51.0

 
> Regards,
> Klara Modin
> 

-- 
Sincerely yours,
Mike.