On 12.01.21 10:34, Dan Williams wrote:
> pfn_section_valid() determines pfn validity on subsection granularity.
>
> pfn_valid_within() internally uses pfn_section_valid(), but gates it
> with early_section() to preserve the traditional behavior of pfn_valid()
> before subsection support was added.
>
> pfn_to_online_page() wants the explicit precision that pfn_valid() does
> not offer, so use pfn_section_valid() directly. Since
> pfn_to_online_page() already open codes the validity of the section
> number vs NR_MEM_SECTIONS, there's not much value to using
> pfn_valid_within(), just use pfn_section_valid(). This loses the
> valid_section() check that pfn_valid_within() was performing, but that
> was already redundant with the online check.
>
> Fixes: b13bc35193d9 ("mm/hotplug: invalid PFNs from pfn_to_online_page()")
> Cc: Qian Cai <cai@xxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Reported-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
> mm/memory_hotplug.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 55a69d4396e7..a845b3979bc0 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -308,11 +308,19 @@ 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;
> +
> + if (!pfn_section_valid(ms, pfn))
> + return NULL;
That's not sufficient for alternative implementations of pfn_valid().
You still need some kind of pfn_valid(pfn) for alternative versions of
pfn_valid(). Consider arm64 memory holes in the memmap. See their
current (yet to be fixed/reworked) pfn_valid() implementation.
(pfn_valid_within() is implicitly active on arm64)
Actually, I think we should add something like the following, to make
this clearer (pfn_valid_within() is confusing)
#ifdef CONFIG_HAVE_ARCH_PFN_VALID
/* We might have to check for holes inside the memmap. */
if (!pfn_valid())
return NULL;
#endif
>
> - if (nr < NR_MEM_SECTIONS && online_section_nr(nr) &&
> - pfn_valid_within(pfn))
> - return pfn_to_page(pfn);
> - return NULL;
> + return pfn_to_page(pfn);
> }
> EXPORT_SYMBOL_GPL(pfn_to_online_page);
>
>
--
Thanks,
David / dhildenb
