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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Wed, 19 Feb 2020 08:37:25 -0800
Message-ID: <CAPcyv4isoKSo2TtP3_VzdPQwdfc2O=KAv44LkqSSTccP7Cnh7A@mail.gmail.com>
Subject: Re: [PATCH v2 RESEND] mm/sparsemem: pfn_to_page is not valid yet on SPARSEMEM
To:     Mike Rapoport <rppt@linux.ibm.com>
Cc:     Baoquan He <bhe@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Wei Yang <richardw.yang@linux.intel.com>,
        David Hildenbrand <david@redhat.com>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>
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On Wed, Feb 19, 2020 at 12:57 AM Mike Rapoport <rppt@linux.ibm.com> wrote:
>
> On Tue, Feb 18, 2020 at 07:25:15PM -0800, Dan Williams wrote:
> > On Tue, Feb 18, 2020 at 7:05 PM Baoquan He <bhe@redhat.com> wrote:
> > >
> > > From: Wei Yang <richardw.yang@linux.intel.com>
> > >
> > > When we use SPARSEMEM instead of SPARSEMEM_VMEMMAP, pfn_to_page()
> > > doesn't work before sparse_init_one_section() is called. This leads to a
> > > crash when hotplug memory:
> >
> > I'd also add:
> >
> > "On x86 the impact is limited to x86_32 builds, or x86_64
> > configurations that override the default setting for
> > SPARSEMEM_VMEMMAP".
>
> Do we also want to check how it affects, say, arm64, ia64 and ppc? ;-)

Sure, I just did not take the time to look up their respective default
stances on SPARSEMEM_VMEMMAP. For a distro looking to backport this
commit I think it's helpful for them to understand if they are exposed
or not.