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

[David Hildenbrand]

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@xxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Oscar Salvador <osalvador@xxxxxxx>
> Reported-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>  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@xxxxxxxxxx>

-- 
Thanks,

David / dhildenb