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From:   Zhaoyang Huang <huangzhaoyang@gmail.com>
Date:   Sun, 18 Aug 2019 15:46:51 +0800
Message-ID: <CAGWkznEvHE6B+eLnCn=s8Hgm3FFbbXcEdj_OxCM4NOj0u61FGA@mail.gmail.com>
Subject: Re: [PATCH] arch : arm : add a criteria for pfn_valid
To:     Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Zhaoyang Huang <zhaoyang.huang@unisoc.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Rob Herring <robh@kernel.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Doug Berger <opendmb@gmail.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Sun, Aug 18, 2019 at 2:32 AM Russell King - ARM Linux admin
<linux@armlinux.org.uk> wrote:
>
> On Sat, Aug 17, 2019 at 11:00:13AM +0800, Zhaoyang Huang wrote:
> > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
> >
> > pfn_valid can be wrong while the MSB of physical address be trimed as pfn
> > larger than the max_pfn.
>
> What scenario are you addressing here?  At a guess, you're addressing
> the non-LPAE case with PFNs that correspond with >= 4GiB of memory?
Please find bellowing for the callstack caused by this defect. The
original reason is a invalid PFN passed from userspace which will
introduce a invalid page within stable_page_flags and then kernel
panic.

[46886.723249] c7 [<c031ff98>] (stable_page_flags) from [<c03203f8>]
(kpageflags_read+0x90/0x11c)
[46886.723256] c7  r9:c101ce04 r8:c2d0bf70 r7:c2d0bf70 r6:1fbb10fb
r5:a8686f08 r4:a8686f08
[46886.723264] c7 [<c0320368>] (kpageflags_read) from [<c0312030>]
(proc_reg_read+0x80/0x94)
[46886.723270] c7  r10:000000b4 r9:00000008 r8:c2d0bf70 r7:00000000
r6:00000001 r5:ed8e7240
[46886.723272] c7  r4:00000000
[46886.723280] c7 [<c0311fb0>] (proc_reg_read) from [<c02a6e6c>]
(__vfs_read+0x48/0x150)
[46886.723284] c7  r7:c2d0bf70 r6:c0f09208 r5:c0a4f940 r4:c40326c0
[46886.723290] c7 [<c02a6e24>] (__vfs_read) from [<c02a7018>]
(vfs_read+0xa4/0x158)
[46886.723296] c7  r9:a8686f08 r8:00000008 r7:c2d0bf70 r6:a8686f08
r5:c40326c0 r4:00000008
[46886.723301] c7 [<c02a6f74>] (vfs_read) from [<c02a778c>]
(SyS_pread64+0x80/0xb8)
[46886.723306] c7  r8:00000008 r7:c0f09208 r6:c40326c0 r5:c40326c0 r4:fdd887d8
[46886.723315] c7 [<c02a770c>] (SyS_pread64) from [<c0108620>]
(ret_fast_syscall+0x0/0x28)

>
> >
> > Signed-off-by: Zhaoyang Huang <huangzhaoyang@gmail.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
> >
> >
>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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