From: Dan Williams <dan.j.williams@xxxxxxxxx> Subject: mm: teach pfn_to_online_page() to consider subsection validity pfn_to_online_page is primarily used to filter out offline or fully uninitialized pages. pfn_valid resp. online_section_nr have a coarse per memory section granularity. If a section shared with a partially offline memory (e.g. part of ZONE_DEVICE) then pfn_to_online_page would lead to a false positive on some pfns. Fix this by adding pfn_section_valid check which is subsection aware. [mhocko@xxxxxxxxxx: changelog rewrite] Link: https://lkml.kernel.org/r/161058500148.1840162.4365921007820501696.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Fixes: b13bc35193d9 ("mm/hotplug: invalid PFNs from pfn_to_online_page()") Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> Reported-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Qian Cai <cai@xxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memory_hotplug.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) --- a/mm/memory_hotplug.c~mm-teach-pfn_to_online_page-to-consider-subsection-validity +++ a/mm/memory_hotplug.c @@ -308,11 +308,26 @@ static int check_hotplug_memory_addressa 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 && online_section_nr(nr) && - pfn_valid_within(pfn)) - return pfn_to_page(pfn); - return NULL; + 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) && !pfn_valid(pfn)) + return NULL; + + if (!pfn_section_valid(ms, pfn)) + return NULL; + + return pfn_to_page(pfn); } EXPORT_SYMBOL_GPL(pfn_to_online_page); _
