linux-kernel - Re: [PATCH] mm/sparse: only sub-section aligned range would be populated

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Message-ID: <f1e6036c-1966-56dd-0acf-e795671c5ec4@redhat.com>
Date:   Tue, 30 Jun 2020 14:52:35 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Wei Yang <richard.weiyang@...ux.alibaba.com>,
        dan.j.williams@...el.com, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/sparse: only sub-section aligned range would be
 populated

On 30.06.20 04:14, Wei Yang wrote:
> There are two code path which invoke __populate_section_memmap()
> 
>   * sparse_init_nid()
>   * sparse_add_section()
> 
> For both case, we are sure the memory range is sub-section aligned.
> 
>   * we pass PAGES_PER_SECTION to sparse_init_nid()
>   * we check range by check_pfn_span() before calling
>     sparse_add_section()
> 
> Also, the counterpart of __populate_section_memmap(), we don't do such
> calculation and check since the range is checked by check_pfn_span() in
> __remove_pages().
> 
> Clear the calculation and check to keep it simple and comply with its
> counterpart.
> 
> Signed-off-by: Wei Yang <richard.weiyang@...ux.alibaba.com>
> ---
>  mm/sparse-vmemmap.c | 16 ++--------------
>  1 file changed, 2 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
> index 0db7738d76e9..24b01ebae111 100644
> --- a/mm/sparse-vmemmap.c
> +++ b/mm/sparse-vmemmap.c
> @@ -247,20 +247,8 @@ int __meminit vmemmap_populate_basepages(unsigned long start,
>  struct page * __meminit __populate_section_memmap(unsigned long pfn,
>  		unsigned long nr_pages, int nid, struct vmem_altmap *altmap)
>  {
> -	unsigned long start;
> -	unsigned long end;
> -
> -	/*
> -	 * The minimum granularity of memmap extensions is
> -	 * PAGES_PER_SUBSECTION as allocations are tracked in the
> -	 * 'subsection_map' bitmap of the section.
> -	 */
> -	end = ALIGN(pfn + nr_pages, PAGES_PER_SUBSECTION);
> -	pfn &= PAGE_SUBSECTION_MASK;
> -	nr_pages = end - pfn;
> -
> -	start = (unsigned long) pfn_to_page(pfn);
> -	end = start + nr_pages * sizeof(struct page);
> +	unsigned long start = (unsigned long) pfn_to_page(pfn);
> +	unsigned long end = start + nr_pages * sizeof(struct page);
>  
>  	if (vmemmap_populate(start, end, nid, altmap))
>  		return NULL;
> 

Can we add a WARN_ON_ONCE to catch mis-use in the future?

if (WARN_ON_ONCE(!IS_ALIGNED(pfn, PAGES_PER_SUBSECTION) ||
                 !IS_ALIGNED(nr_pages, PAGES_PER_SUBSECTION))
	return NULL;

-- 
Thanks,

David / dhildenb