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

[Mike Rapoport]

On Thu, Apr 16, 2026 at 10:10:06AM +0200, Thomas Weißschuh wrote:
> Hi Mike,
> 
> On Wed, Feb 11, 2026 at 12:31:40PM +0200, Mike Rapoport wrote:
> > From: "Mike Rapoport (Microsoft)" <rppt@xxxxxxxxxx>
> > 
> > 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.

Hmm, looks like sh does not like boot_param_page declared as unsigned char *
This fixes the issue for me:

diff --git a/arch/sh/include/asm/setup.h b/arch/sh/include/asm/setup.h
index 63c9efc06348..b7c4469cb61e 100644
--- a/arch/sh/include/asm/setup.h
+++ b/arch/sh/include/asm/setup.h
@@ -3,12 +3,13 @@
 #define _SH_SETUP_H
 
 #include <uapi/asm/setup.h>
+#include <asm/page.h>
 
 /*
  * This is set up by the setup-routine at boot-time
  */
-extern unsigned char *boot_params_page;
-#define PARAM boot_params_page
+extern unsigned long boot_params_page[PAGE_SIZE / sizeof(unsigned long)];
+#define PARAM ((unsigned char *)boot_params_page)
 
 #define MOUNT_ROOT_RDONLY (*(unsigned long *) (PARAM+0x000))
 #define RAMDISK_FLAGS (*(unsigned long *) (PARAM+0x004))
 
> 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

-- 
Sincerely yours,
Mike.