linux-kernel - Re: [PATCH v2 10/13] arch, mm: set high_memory in free_area

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Message-ID: <20250402140521-bf9b3743-094e-4097-a189-10cdf1db9255@linutronix.de>
Date: Wed, 2 Apr 2025 14:19:01 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Mike Rapoport <rppt@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>, Ard Biesheuvel <ardb@...nel.org>, 
	Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "David S. Miller" <davem@...emloft.net>, 
	Geert Uytterhoeven <geert@...ux-m68k.org>, Ingo Molnar <mingo@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, 
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org, 
	Naresh Kamboju <naresh.kamboju@...aro.org>, lkft-triage@...ts.linaro.org, 
	Linux Regressions <regressions@...ts.linux.dev>
Subject: Re: [PATCH v2 10/13] arch, mm: set high_memory in free_area_init()

(drop all the non-x86 and non-mm recipients)

Hi,

On Thu, Mar 13, 2025 at 03:50:00PM +0200, Mike Rapoport wrote:
> From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
> 
> high_memory defines upper bound on the directly mapped memory.
> This bound is defined by the beginning of ZONE_HIGHMEM when a system has
> high memory and by the end of memory otherwise.
> 
> All this is known to generic memory management initialization code that
> can set high_memory while initializing core mm structures.
> 
> Add a generic calculation of high_memory to free_area_init() and remove
> per-architecture calculation except for the architectures that set and
> use high_memory earlier than that.

This change (in mainline as commit e120d1bc12da ("arch, mm: set high_memory in free_area_init()")
breaks booting i386 on QEMU for me (and others [0]).
The boot just hangs without output.

It's easily reproducible with kunit:
./tools/testing/kunit/kunit.py run --arch i386

See below for the specific problematic hunk.

[0] https://lore.kernel.org/lkml/CA+G9fYtdXHVuirs3v6at3UoKNH5keuq0tpcvpz0tJFT4toLG4g@mail.gmail.com/

> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>	# x86
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> ---
>  arch/alpha/mm/init.c         |  1 -
>  arch/arc/mm/init.c           |  2 --
>  arch/arm64/mm/init.c         |  2 --
>  arch/csky/mm/init.c          |  1 -
>  arch/hexagon/mm/init.c       |  6 ------
>  arch/loongarch/kernel/numa.c |  1 -
>  arch/loongarch/mm/init.c     |  2 --
>  arch/microblaze/mm/init.c    |  2 --
>  arch/mips/mm/init.c          |  2 --
>  arch/nios2/mm/init.c         |  6 ------
>  arch/openrisc/mm/init.c      |  2 --
>  arch/parisc/mm/init.c        |  1 -
>  arch/riscv/mm/init.c         |  1 -
>  arch/s390/mm/init.c          |  2 --
>  arch/sh/mm/init.c            |  7 -------
>  arch/sparc/mm/init_32.c      |  1 -
>  arch/sparc/mm/init_64.c      |  2 --
>  arch/um/kernel/um_arch.c     |  1 -
>  arch/x86/kernel/setup.c      |  2 --
>  arch/x86/mm/init_32.c        |  3 ---
>  arch/x86/mm/numa_32.c        |  3 ---
>  arch/xtensa/mm/init.c        |  2 --
>  mm/memory.c                  |  8 --------
>  mm/mm_init.c                 | 30 ++++++++++++++++++++++++++++++
>  mm/nommu.c                   |  2 --
>  25 files changed, 30 insertions(+), 62 deletions(-)

<snip>

> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
> index 6d2f8cb9451e..801b659ead0c 100644
> --- a/arch/x86/mm/init_32.c
> +++ b/arch/x86/mm/init_32.c
> @@ -643,9 +643,6 @@ void __init initmem_init(void)
>  		highstart_pfn = max_low_pfn;
>  	printk(KERN_NOTICE "%ldMB HIGHMEM available.\n",
>  		pages_to_mb(highend_pfn - highstart_pfn));
> -	high_memory = (void *) __va(highstart_pfn * PAGE_SIZE - 1) + 1;
> -#else
> -	high_memory = (void *) __va(max_low_pfn * PAGE_SIZE - 1) + 1;
>  #endif

Reverting this hunk fixes the issue for me.

>  
>  	memblock_set_node(0, PHYS_ADDR_MAX, &memblock.memory, 0);