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

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Message-ID: <Z-0xrWyff9-9bJRf@kernel.org>
Date: Wed, 2 Apr 2025 15:46:37 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
	Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
	"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()

On Wed, Apr 02, 2025 at 02:19:01PM +0200, Thomas Weißschuh wrote:
> (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/
> 
> 
> > 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.
 
This is already done by d893aca973c3 ("x86/mm: restore early initialization
of high_memory for 32-bits").
  
> >  	memblock_set_node(0, PHYS_ADDR_MAX, &memblock.memory, 0);

-- 
Sincerely yours,
Mike.