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Date:   Fri, 7 Feb 2020 11:50:23 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Wei Yang <richardw.yang@linux.intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Oscar Salvador <osalvador@suse.de>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH 3/3] mm/sparsemem: avoid memmap overwrite for
 non-SPARSEMEM_VMEMMAP
Message-ID: <20200207035023.GT8965@MiWiFi-R3L-srv>
References: <20200206231629.14151-1-richardw.yang@linux.intel.com>
 <20200206231629.14151-4-richardw.yang@linux.intel.com>
 <CAPcyv4hLW5Ww1Bo0MmNi8fzUNQEvudtWpGOK23MWaiqQ+MemfA@mail.gmail.com>
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On 02/06/20 at 06:06pm, Dan Williams wrote:
> On Thu, Feb 6, 2020 at 3:17 PM Wei Yang <richardw.yang@linux.intel.com> wrote:
> >
> > In case of SPARSEMEM, populate_section_memmap() would allocate memmap
> > for the whole section, even we just want a sub-section. This would lead
> > to memmap overwrite if we a sub-section to an already populated section.
> >
> > Just return the populated memmap for non-SPARSEMEM_VMEMMAP case.
> >
> > Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
> > Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> > CC: Dan Williams <dan.j.williams@intel.com>
> > ---
> >  mm/sparse.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/mm/sparse.c b/mm/sparse.c
> > index 56816f653588..c75ca40db513 100644
> > --- a/mm/sparse.c
> > +++ b/mm/sparse.c
> > @@ -836,6 +836,16 @@ static struct page * __meminit section_activate(int nid, unsigned long pfn,
> >         if (nr_pages < PAGES_PER_SECTION && early_section(ms))
> >                 return pfn_to_page(pfn);
> >
> > +       /*
> > +        * If it is not SPARSEMEM_VMEMMAP, we always populate memmap for the
> > +        * whole section, even for a sub-section.
> > +        *
> > +        * Return its memmap if already populated to avoid memmap overwrite.
> > +        */
> > +       if (!IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) &&
> > +               valid_section(ms))
> > +               return __section_mem_map_addr(ms);
> 
> Again, is check_pfn_span() failing to prevent this path?

The answer should be yes, this patch is not needed.

>