arch, mm: consolidate empty_zero_page

Reduce 22 declarations of empty_zero_page to 3 and 23 declarations of
ZERO_PAGE() to 4.

Every architecture defines empty_zero_page that way or another, but for the
most of them it is always a page aligned page in BSS and most definitions
of ZERO_PAGE do virt_to_page(empty_zero_page).

Move Linus vetted x86 definition of empty_zero_page and ZERO_PAGE() to the
core MM and drop these definitions in architectures that do not implement
colored zero page (MIPS and s390).

ZERO_PAGE() remains a macro because turning it to a wrapper for a static
inline causes severe pain in header dependencies.

For the most part the change is mechanical, with these being noteworthy:

* alpha: aliased empty_zero_page with ZERO_PGE that was also used for boot
  parameters. Switching to a generic empty_zero_page removes the aliasing
  and keeps ZERO_PGE for boot parameters only
* arm64: uses __pa_symbol() in ZERO_PAGE() so that definition of
  ZERO_PAGE() is kept intact.
* m68k/parisc/um: allocated empty_zero_page from memblock,
  although they do not support zero page coloring and having it in BSS
  will work fine.
* sparc64 can have empty_zero_page in BSS rather allocate it, but it
  can't use virt_to_page() for BSS. Keep it's definition of ZERO_PAGE()
  but instead of allocating it, make mem_map_zero point to
  empty_zero_page.
* sh: used empty_zero_page for boot parameters at the very early boot.
  Rename the parameters page to boot_params_page and let sh use the generic
  empty_zero_page.
* hexagon: had an amusing comment about empty_zero_page

	/* A handy thing to have if one has the RAM. Declared in head.S */

  that unfortunately had to go :)

Link: https://lkml.kernel.org/r/20260211103141.3215197-4-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Helge Deller <deller@gmx.de>		[parisc]
Tested-by: Helge Deller <deller@gmx.de>		[parisc]
Reviewed-by: Christophe Leroy (CS GROUP) <chleroy@kernel.org>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Magnus Lindholm <linmag7@gmail.com>	[alpha]
Acked-by: Dinh Nguyen <dinguyen@kernel.org>	[nios2]
Acked-by: Andreas Larsson <andreas@gaisler.com>	[sparc]
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: David S. Miller <davem@davemloft.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Guo Ren <guoren@kernel.org>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Stafford Horne <shorne@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vineet Gupta <vgupta@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/alpha/include/asm/pgtable.h

@@ -126,12 +126,6 @@ struct vm_area_struct;
  */
 #define pgprot_noncached(prot)	(prot)
 
-/*
- * ZERO_PAGE is a global shared page that is always zero:  used
- * for zero-mapped memory areas etc..
- */
-#define ZERO_PAGE(vaddr)	(virt_to_page(ZERO_PGE))
-
 /*
  * On certain platforms whose physical address space can overlap KSEG,
  * namely EV6 and above, we must re-twiddle the physaddr to restore the

arch/arc/include/asm/pgtable.h

@@ -21,9 +21,6 @@
 
 #ifndef __ASSEMBLER__
 
-extern char empty_zero_page[PAGE_SIZE];
-#define ZERO_PAGE(vaddr)	(virt_to_page(empty_zero_page))
-
 extern pgd_t swapper_pg_dir[] __aligned(PAGE_SIZE);
 
 /* to cope with aliasing VIPT cache */

arch/arc/mm/init.c

@@ -19,8 +19,6 @@
 #include <asm/arcregs.h>
 
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __aligned(PAGE_SIZE);
-char empty_zero_page[PAGE_SIZE] __aligned(PAGE_SIZE);
-EXPORT_SYMBOL(empty_zero_page);
 
 static const unsigned long low_mem_start = CONFIG_LINUX_RAM_BASE;
 static unsigned long low_mem_sz;

arch/arm/include/asm/pgtable.h

@@ -10,15 +10,6 @@
 #include <linux/const.h>
 #include <asm/proc-fns.h>
 
-#ifndef __ASSEMBLY__
-/*
- * ZERO_PAGE is a global shared page that is always zero: used
- * for zero-mapped memory areas etc..
- */
-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>
 
 #ifndef CONFIG_MMU

arch/arm/mm/mmu.c

@@ -41,13 +41,6 @@
 
 extern unsigned long __atags_pointer;
 
-/*
- * empty_zero_page is a special page that is used for
- * zero-initialized data and COW.
- */
-unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
-EXPORT_SYMBOL(empty_zero_page);
-
 /*
  * The pmd table for the upper-most set of pages.
  */

arch/arm/mm/nommu.c

@@ -27,13 +27,6 @@
 
 unsigned long vectors_base;
 
-/*
- * empty_zero_page is a special page that is used for
- * zero-initialized data and COW.
- */
-unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
-EXPORT_SYMBOL(empty_zero_page);
-
 #ifdef CONFIG_ARM_MPU
 struct mpu_rgn_info mpu_rgn_info;
 #endif

arch/arm64/include/asm/pgtable.h

@@ -110,7 +110,6 @@ static inline void arch_leave_lazy_mmu_mode(void)
  * ZERO_PAGE is a global shared page that is always zero: used
  * for zero-mapped memory areas etc..
  */
-extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 #define ZERO_PAGE(vaddr)	phys_to_page(__pa_symbol(empty_zero_page))
 
 #define pte_ERROR(e)	\

arch/arm64/mm/mmu.c

@@ -64,13 +64,6 @@ static bool rodata_is_rw __ro_after_init = true;
  */
 long __section(".mmuoff.data.write") __early_cpu_boot_status;
 
-/*
- * Empty_zero_page is a special page that is used for zero-initialized data
- * and COW.
- */
-unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
-EXPORT_SYMBOL(empty_zero_page);
-
 static DEFINE_SPINLOCK(swapper_pgdir_lock);
 static DEFINE_MUTEX(fixmap_lock);
 

arch/csky/include/asm/pgtable.h

@@ -76,9 +76,6 @@
 #define MAX_SWAPFILES_CHECK() \
 		BUILD_BUG_ON(MAX_SWAPFILES_SHIFT != 5)
 
-extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
-#define ZERO_PAGE(vaddr)	(virt_to_page(empty_zero_page))
-
 extern void load_pgd(unsigned long pg_dir);
 extern pte_t invalid_pte_table[PTRS_PER_PTE];
 

arch/csky/mm/init.c

@@ -38,9 +38,6 @@ pte_t invalid_pte_table[PTRS_PER_PTE] __page_aligned_bss;
 pte_t kernel_pte_tables[PTRS_KERN_TABLE] __page_aligned_bss;
 
 EXPORT_SYMBOL(invalid_pte_table);
-unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
-						__page_aligned_bss;
-EXPORT_SYMBOL(empty_zero_page);
 
 void free_initmem(void)
 {

arch/hexagon/include/asm/pgtable.h

@@ -14,9 +14,6 @@
 #include <asm/page.h>
 #include <asm-generic/pgtable-nopmd.h>
 
-/* A handy thing to have if one has the RAM. Declared in head.S */
-extern unsigned long empty_zero_page;
-
 /*
  * The PTE model described here is that of the Hexagon Virtual Machine,
  * which autonomously walks 2-level page tables.  At a lower level, we
@@ -348,9 +345,6 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd)
 	return (unsigned long)__va(pmd_val(pmd) & PAGE_MASK);
 }
 
-/* ZERO_PAGE - returns the globally shared zero page */
-#define ZERO_PAGE(vaddr) (virt_to_page(&empty_zero_page))
-
 /*
  * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
  * are !pte_none() && !pte_present().

arch/hexagon/kernel/head.S

@@ -216,8 +216,3 @@ __head_s_vaddr_target:
 .p2align PAGE_SHIFT
 ENTRY(external_cmdline_buffer)
         .fill _PAGE_SIZE,1,0
-
-.data
-.p2align PAGE_SHIFT
-ENTRY(empty_zero_page)
-        .fill _PAGE_SIZE,1,0

arch/hexagon/kernel/hexagon_ksyms.c

@@ -17,7 +17,6 @@ EXPORT_SYMBOL(raw_copy_to_user);
 EXPORT_SYMBOL(__vmgetie);
 EXPORT_SYMBOL(__vmsetie);
 EXPORT_SYMBOL(__vmyield);
-EXPORT_SYMBOL(empty_zero_page);
 EXPORT_SYMBOL(memcpy);
 EXPORT_SYMBOL(memset);
 

arch/loongarch/include/asm/pgtable.h

@@ -74,15 +74,6 @@
 struct mm_struct;
 struct vm_area_struct;
 
-/*
- * ZERO_PAGE is a global shared page that is always zero; used
- * for zero-mapped memory areas etc..
- */
-
-extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
-
-#define ZERO_PAGE(vaddr)	virt_to_page(empty_zero_page)
-
 #ifdef CONFIG_32BIT
 
 #define VMALLOC_START	(vm_map_base + PCI_IOSIZE + (2 * PAGE_SIZE))

arch/loongarch/mm/init.c

@@ -36,9 +36,6 @@
 #include <asm/pgalloc.h>
 #include <asm/tlb.h>
 
-unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
-EXPORT_SYMBOL(empty_zero_page);
-
 void copy_user_highpage(struct page *to, struct page *from,
 	unsigned long vaddr, struct vm_area_struct *vma)
 {

arch/m68k/include/asm/pgtable_mm.h

@@ -110,15 +110,6 @@ extern unsigned long m68k_vmalloc_end;
 #define VMALLOC_END KMAP_START
 #endif
 
-/* zero page used for uninitialized stuff */
-extern void *empty_zero_page;
-
-/*
- * ZERO_PAGE is a global shared page that is always zero: used
- * for zero-mapped memory areas etc..
- */
-#define ZERO_PAGE(vaddr)	(virt_to_page(empty_zero_page))
-
 extern void kernel_set_cachemode(void *addr, unsigned long size, int cmode);
 
 /*

arch/m68k/include/asm/pgtable_no.h

@@ -30,13 +30,6 @@
 
 #define swapper_pg_dir ((pgd_t *) 0)
 
-/*
- * ZERO_PAGE is a global shared page that is always zero: used
- * for zero-mapped memory areas etc..
- */
-extern void *empty_zero_page;
-#define ZERO_PAGE(vaddr)	(virt_to_page(empty_zero_page))
-
 /*
  * All 32bit addresses are effectively valid for vmalloc...
  * Sort of meaningless for non-VM targets.

arch/m68k/mm/init.c

@@ -33,13 +33,6 @@
 #include <asm/sections.h>
 #include <asm/tlb.h>
 
-/*
- * ZERO_PAGE is a special page that is used for zero-initialized
- * data and COW.
- */
-void *empty_zero_page;
-EXPORT_SYMBOL(empty_zero_page);
-
 void __init arch_zone_limits_init(unsigned long *max_zone_pfns)
 {
 	max_zone_pfns[ZONE_DMA] = PFN_DOWN(memblock_end_of_DRAM());
@@ -71,8 +64,6 @@ void __init paging_init(void)
 	unsigned long end_mem = memory_end & PAGE_MASK;
 
 	high_memory = (void *) end_mem;
-
-	empty_zero_page = memblock_alloc_or_panic(PAGE_SIZE, PAGE_SIZE);
 }
 
 #endif /* CONFIG_MMU */

arch/m68k/mm/mcfmmu.c

@@ -41,8 +41,6 @@ void __init paging_init(void)
 	unsigned long next_pgtable;
 	int i;
 
-	empty_zero_page = memblock_alloc_or_panic(PAGE_SIZE, PAGE_SIZE);
-
 	pg_dir = swapper_pg_dir;
 	memset(swapper_pg_dir, 0, sizeof(swapper_pg_dir));
 

arch/m68k/mm/motorola.c

@@ -498,12 +498,6 @@ void __init paging_init(void)
 
 	early_memtest(min_addr, max_addr);
 
-	/*
-	 * initialize the bad page table and bad page to point
-	 * to a couple of allocated pages
-	 */
-	empty_zero_page = memblock_alloc_or_panic(PAGE_SIZE, PAGE_SIZE);
-
 	/*
 	 * Set up SFC/DFC registers
 	 */