linux-kernel - Re: [PATCH] arm64: mm: fix max_mapnr is assigned the wrong value

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Date:   Mon, 1 Apr 2019 11:44:32 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Muchun Song <smuchun@...il.com>
Cc:     will.deacon@....com, akpm@...ux-foundation.org,
        rppt@...ux.vnet.ibm.com, ard.biesheuvel@...aro.org,
        f.fainelli@...il.com, logang@...tatee.com, robin.murphy@....com,
        ghackmann@...roid.com, hannes@...xchg.org, stefan@...er.ch,
        david@...hat.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: mm: fix max_mapnr is assigned the wrong value

On Sat, Mar 30, 2019 at 09:13:46PM +0800, Muchun Song wrote:
> When we not use flat memory, the mem_map will be NULL and
> pfn_to_page(max_pfn) is a pointer which is located in kernel space. So
> max_mapnr is assigned a very large number(e.g., 0xffffxxxx_xxxxxxxx) - fix
> it.
> 
> Signed-off-by: Muchun Song <smuchun@...il.com>
> ---
>  arch/arm64/mm/init.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index bc02818fa48b..e86c21a44c88 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -535,7 +535,7 @@ void __init mem_init(void)
>  	else
>  		swiotlb_force = SWIOTLB_NO_FORCE;
>  
> -	set_max_mapnr(pfn_to_page(max_pfn) - mem_map);
> +	set_max_mapnr(max_pfn - PHYS_PFN_OFFSET);
>  
>  #ifndef CONFIG_SPARSEMEM_VMEMMAP
>  	free_unused_memmap();

The patch looks fine but did you actually hit any problem? max_mapnr
seems to only be used in the generic pfn_valid() which we do not use on
arm64 (just wondering if it needs a cc stable; it doesn't look like as
it's not a regression).

-- 
Catalin