linux-kernel - Re: [PATCH] arch : arm : add a criteria for pfn

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Message-Id: <20190817090021.GA10627@rapoport-lnx>
Date:   Sat, 17 Aug 2019 12:00:22 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        Russell King <linux@...linux.org.uk>,
        Rob Herring <robh@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Doug Berger <opendmb@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch : arm : add a criteria for pfn_valid

On Sat, Aug 17, 2019 at 11:00:13AM +0800, Zhaoyang Huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> 
> pfn_valid can be wrong while the MSB of physical address be trimed as pfn
> larger than the max_pfn.

How the overflow of __pfn_to_phys() is related to max_pfn?
Where is the guarantee that __pfn_to_phys(max_pfn) won't overflow?
 
> Signed-off-by: Zhaoyang Huang <huangzhaoyang@...il.com>
> ---
>  arch/arm/mm/init.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index c2daabb..9c4d938 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -177,7 +177,8 @@ static void __init zone_sizes_init(unsigned long min, unsigned long max_low,
>  #ifdef CONFIG_HAVE_ARCH_PFN_VALID
>  int pfn_valid(unsigned long pfn)
>  {
> -	return memblock_is_map_memory(__pfn_to_phys(pfn));
> +	return (pfn > max_pfn) ?
> +		false : memblock_is_map_memory(__pfn_to_phys(pfn));
>  }
>  EXPORT_SYMBOL(pfn_valid);
>  #endif
> -- 
> 1.9.1
> 

-- 
Sincerely yours,
Mike.