Re: [PATCH v3 3/4] arch, mm: consolidate empty_zero_page

Magnus Lindholm
2026-02-11T20:14:44Z

On Wed, Feb 11, 2026 at 11:32 AM Mike Rapoport <rppt@kernel.org> wrote:
>
> From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
>
> 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 :)
>
> 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>
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
> arch/alpha/include/asm/pgtable.h | 6 ------

> diff --git a/arch/alpha/include/asm/pgtable.h b/arch/alpha/include/asm/pgtable.h
> index 90e7a9539102..12a3c5f8ece8 100644
> --- a/arch/alpha/include/asm/pgtable.h
> +++ b/arch/alpha/include/asm/pgtable.h
> @@ -125,12 +125,6 @@ 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

This looks good from an Alpha perspective

Acked-by: Magnus Lindholm <linmag7@gmail.com>