On Mon 02-04-18 09:50:26, Wei Yang wrote:
> On Fri, Mar 30, 2018 at 01:57:27PM -0700, Andrew Morton wrote:
> >On Fri, 30 Mar 2018 11:30:55 +0800 Wei Yang <richard.weiyang@xxxxxxxxx> wrote:
> >
> >> memblock_search_pfn_nid() returns the nid and the [start|end]_pfn of the
> >> memory region where pfn sits in. While the calculation of start_pfn has
> >> potential issue when the regions base is not page aligned.
> >>
> >> For example, we assume PAGE_SHIFT is 12 and base is 0x1234. Current
> >> implementation would return 1 while this is not correct.
> >
> >Why is this not correct? The caller might want the pfn of the page
> >which covers the base?
> >
>
> Hmm... the only caller of memblock_search_pfn_nid() is __early_pfn_to_nid(),
> which returns the nid of a pfn and save the [start_pfn, end_pfn] with in the
> same memory region to a cache. So this looks not a good practice to store
> un-exact pfn in the cache.
>
> >> This patch fixes this by using PFN_UP().
> >>
> >> The original commit is commit e76b63f80d93 ("memblock, numa: binary search
> >> node id") and merged in v3.12.
> >>
> >> Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
> >> Cc: 3.12+ <stable@xxxxxxxxxxxxxxx>
> >
> >Please fully describe the runtime effects of a bug when fixing that
> >bug. This description doesn't give enough justification for merging
> >the patch into mainline, let alone -stable.
>
> Since PFN_UP() and PFN_DOWN() differs when the address is not page aligned, in
> theory we may have two situations like below.
Have you ever seen a HW that would report page unaligned memory ranges?
Is this even possible?
--
Michal Hocko
SUSE Labs
