linux-kernel - Re: [PATCH v3 2/6] mm: Teach pfn_to_online_page() to consider subsection validity

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Date:   Wed, 13 Jan 2021 13:52:14 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Linux MM <linux-mm@...ck.org>, Qian Cai <cai@....pw>,
        Michal Hocko <mhocko@...e.com>,
        Oscar Salvador <osalvador@...e.de>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 2/6] mm: Teach pfn_to_online_page() to consider
 subsection validity

On Wed, Jan 13, 2021 at 12:29 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 13.01.21 08:35, Dan Williams wrote:
> > pfn_section_valid() determines pfn validity on subsection granularity
> > where pfn_valid() may be limited to coarse section granularity.
> > Explicitly validate subsections after pfn_valid() succeeds.
> >
> > Fixes: b13bc35193d9 ("mm/hotplug: invalid PFNs from pfn_to_online_page()")
> > Cc: Qian Cai <cai@....pw>
> > Cc: Michal Hocko <mhocko@...e.com>
> > Cc: Oscar Salvador <osalvador@...e.de>
> > Reported-by: David Hildenbrand <david@...hat.com>
> > Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> > ---
> >  mm/memory_hotplug.c |   24 ++++++++++++++++++++----
> >  1 file changed, 20 insertions(+), 4 deletions(-)
> >
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index 55a69d4396e7..9f37f8a68da4 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -308,11 +308,27 @@ static int check_hotplug_memory_addressable(unsigned long pfn,
> >  struct page *pfn_to_online_page(unsigned long pfn)
> >  {
> >       unsigned long nr = pfn_to_section_nr(pfn);
> > +     struct mem_section *ms;
> > +
> > +     if (nr >= NR_MEM_SECTIONS)
> > +             return NULL;
> > +
> > +     ms = __nr_to_section(nr);
> > +     if (!online_section(ms))
> > +             return NULL;
> > +
> > +     /*
> > +      * Save some code text when online_section() +
> > +      * pfn_section_valid() are sufficient.
> > +      */
> > +     if (IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID))
> > +             if (!pfn_valid(pfn))
> > +                     return NULL;
>
> Nit:
>
> if (IS_ENABLED(CONFIG_HAVE_ARCH_PFN_VALID) &&
>     !pfn_valid(pfn))
>

Ok... I'll do a final resend "To: akpm" after the kbuild robot
finishes chewing on this series.