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Subject: Re: [PATCH v3 2/6] mm: Teach pfn_to_online_page() to consider
 subsection validity
To:     Dan Williams <dan.j.williams@intel.com>, linux-mm@kvack.org
Cc:     Qian Cai <cai@lca.pw>, Michal Hocko <mhocko@suse.com>,
        Oscar Salvador <osalvador@suse.de>, vishal.l.verma@intel.com,
        linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org
References: <161052331545.1805594.2356512831689786960.stgit@dwillia2-desk3.amr.corp.intel.com>
 <161052332755.1805594.9846390935351758277.stgit@dwillia2-desk3.amr.corp.intel.com>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <230efa36-9192-fe52-b8b6-16b2feafb70b@redhat.com>
Date:   Wed, 13 Jan 2021 09:29:00 +0100
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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@lca.pw>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Reported-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.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))

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb