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

["Thomas Weißschuh" <thomas.weissschuh@linutronix.de>]

Hi Mike,

On Wed, Feb 11, 2026 at 12:31:40PM +0200, Mike Rapoport 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.

With this in mainline as commit 6215d9f4470f ("arch, mm: consolidate
empty_zero_page") booting sh on QEMU is now broken.
The machine hangs before any output.

Reproducer:
./tools/testing/kunit/kunit.py run --arch sh --cross_compile sh4-linux- --raw_output=all example

> * 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 :)

(...)


Thomas