linux-kernel - Re: [PATCH] memremap: Fix NULL pointer BUG in get_zone_device

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Message-ID: <1471987482.32015.111.camel@hpe.com>
Date:   Tue, 23 Aug 2016 21:25:09 +0000
From:   "Kani, Toshimitsu" <toshi.kani@....com>
To:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "Mulumudi, Abhilash Kumar" <m.abhilash-kumar@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
        "linux-nvdimm@...1.01.org" <linux-nvdimm@...1.01.org>,
        "brian.starkey@....com" <brian.starkey@....com>
Subject: Re: [PATCH] memremap: Fix NULL pointer BUG in get_zone_device_page()

On Tue, 2016-08-23 at 13:42 -0700, Andrew Morton wrote:
> On Tue, 23 Aug 2016 12:43:20 -0600 Toshi Kani <toshi.kani@....com>
> wrote:
> 
> > 
> > The following BUG was observed while starting up KVM with nvdimm
> > device as memory-backend-file to /dev/dax.
> > 
> >  BUG: unable to handle kernel NULL pointer dereference at
> > 0000000000000008
> > 
> > ...
> > 
> > devm_memremap_pages() calls for_each_device_pfn() to walk through
> > all pfns in page_map.  pfn_first(), however, returns a wrong pfn
> > that leaves page->pgmap uninitialized.
> > 
> > Since arch_add_memory() has set up direct mappings to the NVDIMM
> > range with altmap, pfn_first() should not modify the start pfn.
> > Change pfn_first() to simply return pfn of res->start.
> 
> Which kernel version(s) do you think need fixing?

The fix applies to v4.5 and newer versions.

Thanks,
-Toshi