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

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Date:   Sat, 17 Aug 2019 17:14:13 +0800
From:   Zhaoyang Huang <huangzhaoyang@...il.com>
To:     Mike Rapoport <rppt@...ux.ibm.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>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arch : arm : add a criteria for pfn_valid

On Sat, Aug 17, 2019 at 5:00 PM Mike Rapoport <rppt@...ux.ibm.com> wrote:
>
> 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?
eg, the invalid pfn value as 0x1bffc0 will pass pfn_valid if there is
a memory block while the max_pfn is 0xbffc0.
In ARM64, bellowing condition check will help to
>
> > 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.
>