linux-kernel - Re: [PATCH mm-unstable] arch, mm: consolidate empty_zero

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Message-ID: <55bef6c2-de81-4b60-b6df-5ef733b54dee@gaisler.com>
Date: Mon, 9 Feb 2026 09:41:08 +0100
From: Andreas Larsson <andreas@...sler.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Borislav Petkov
 <bp@...en8.de>, Brian Cain <bcain@...nel.org>,
 Catalin Marinas <catalin.marinas@....com>,
 "David S. Miller" <davem@...emloft.net>,
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 Geert Uytterhoeven <geert@...ux-m68k.org>, Guo Ren <guoren@...nel.org>,
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Subject: Re: [PATCH mm-unstable] arch, mm: consolidate empty_zero_page

On 2026-02-07 11:36, Mike Rapoport wrote:
>> Unfortunately, that does not help. The LDOM goes down in the same fashion.
> 
> Apparently something is wrong with my pointer arithmetics :/
> 
> Can you try this one instead?
> 
> diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
> index 74ede706fb32..615f460c50af 100644
> --- a/arch/sparc/include/asm/pgtable_64.h
> +++ b/arch/sparc/include/asm/pgtable_64.h
> @@ -210,6 +210,9 @@ extern unsigned long _PAGE_CACHE;
>  extern unsigned long pg_iobits;
>  extern unsigned long _PAGE_ALL_SZ_BITS;
>  
> +extern struct page *mem_map_zero;
> +#define ZERO_PAGE(vaddr)	(mem_map_zero)
> +
>  /* PFNs are real physical page numbers.  However, mem_map only begins to record
>   * per-page information starting at pfn_base.  This is to handle systems where
>   * the first physical page in the machine is at some huge physical address,
> diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
> index 2bd99944176d..aa1f9f071fb2 100644
> --- a/arch/sparc/mm/init_64.c
> +++ b/arch/sparc/mm/init_64.c
> @@ -177,6 +177,9 @@ extern unsigned long sparc_ramdisk_image64;
>  extern unsigned int sparc_ramdisk_image;
>  extern unsigned int sparc_ramdisk_size;
>  
> +struct page *mem_map_zero __read_mostly;
> +EXPORT_SYMBOL(mem_map_zero);
> +
>  unsigned int sparc64_highest_unlocked_tlb_ent __read_mostly;
>  
>  unsigned long sparc64_kern_pri_context __read_mostly;
> @@ -2495,6 +2498,9 @@ static void __init register_page_bootmem_info(void)
>  }
>  void __init mem_init(void)
>  {
> +	phys_addr_t zero_page_pa = kern_base +
> +		((unsigned long)&empty_zero_page[0] - KERNBASE);
> +
>  	/*
>  	 * Must be done after boot memory is put on freelist, because here we
>  	 * might set fields in deferred struct pages that have not yet been
> @@ -2503,6 +2509,12 @@ void __init mem_init(void)
>  	 */
>  	register_page_bootmem_info();
>  
> +	/*
> +	 * Set up the zero page, mark it reserved, so that page count
> +	 * is not manipulated when freeing the page from user ptes.
> +	 */
> +	mem_map_zero = pfn_to_page(PHYS_PFN(zero_page_pa));
> +
>  	if (tlb_type == cheetah || tlb_type == cheetah_plus)
>  		cheetah_ecache_flush_init();
>  }
> 

With that one, things work fine.

Cheers,
Andreas