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>

5 files changed, 4 insertions, 28 deletions

diff --git a/arch/sparc/include/asm/pgtable_32.h b/arch/sparc/include/asm/pgtable_32.h
index a9f802d1dd64..f89b1250661d 100644
--- a/arch/sparc/include/asm/pgtable_32.h
+++ b/arch/sparc/include/asm/pgtable_32.h
@@ -72,14 +72,6 @@ extern unsigned long phys_base;
 extern unsigned long pfn_base;
 
 /*
- * 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))
-
-/*
  * In general all page table modifications should use the V8 atomic
  * swap instruction.  This insures the mmu and the cpu are in sync
  * with respect to ref/mod bits in the page tables.
diff --git a/arch/sparc/include/asm/setup.h b/arch/sparc/include/asm/setup.h
index 72205684e51e..21bed5514028 100644
--- a/arch/sparc/include/asm/setup.h
+++ b/arch/sparc/include/asm/setup.h
@@ -17,8 +17,6 @@ extern char reboot_command[];
  */
 extern unsigned char boot_cpu_id;
 
-extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
-
 extern int serial_console;
 static inline int con_is_present(void)
 {
diff --git a/arch/sparc/kernel/head_32.S b/arch/sparc/kernel/head_32.S
index 38345460d542..8c320fa25a67 100644
--- a/arch/sparc/kernel/head_32.S
+++ b/arch/sparc/kernel/head_32.S
@@ -57,13 +57,6 @@ sun4e_notsup:
 
 	.align PAGE_SIZE
 
-/* This was the only reasonable way I could think of to properly align
- * these page-table data structures.
- */
-	.globl empty_zero_page
-empty_zero_page:	.skip PAGE_SIZE
-EXPORT_SYMBOL(empty_zero_page)
-
 	.global root_flags
 	.global ram_flags
 	.global root_dev
diff --git a/arch/sparc/mm/init_32.c b/arch/sparc/mm/init_32.c
index fdc93dd12c3e..e0e66f91ceeb 100644
--- a/arch/sparc/mm/init_32.c
+++ b/arch/sparc/mm/init_32.c
@@ -246,10 +246,6 @@ void __init arch_mm_preinit(void)
 		prom_halt();
 	}
 
-
-	/* Saves us work later. */
-	memset((void *)empty_zero_page, 0, PAGE_SIZE);
-
 	i = last_valid_pfn >> ((20 - PAGE_SHIFT) + 5);
 	i += 1;
 	sparc_valid_addr_bitmap = (unsigned long *)
diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
index f46394c46a76..748790998ff5 100644
--- a/arch/sparc/mm/init_64.c
+++ b/arch/sparc/mm/init_64.c
@@ -2492,6 +2492,9 @@ static void __init register_page_bootmem_info(void)
 }
 void __init mem_init(void)
 {
+	phys_addr_t zero_page_pa = kern_base +
+		((unsigned long)&empty_zero_page[0] - KERNBASE);
+
 	/*
 	 * Must be done after boot memory is put on freelist, because here we
 	 * might set fields in deferred struct pages that have not yet been
@@ -2504,13 +2507,7 @@ void __init mem_init(void)
 	 * Set up the zero page, mark it reserved, so that page count
 	 * is not manipulated when freeing the page from user ptes.
 	 */
-	mem_map_zero = alloc_pages(GFP_KERNEL|__GFP_ZERO, 0);
-	if (mem_map_zero == NULL) {
-		prom_printf("paging_init: Cannot alloc zero page.\n");
-		prom_halt();
-	}
-	mark_page_reserved(mem_map_zero);
-
+	mem_map_zero = pfn_to_page(PHYS_PFN(zero_page_pa));
 
 	if (tlb_type == cheetah || tlb_type == cheetah_plus)
 		cheetah_ecache_flush_init();