On Fri 16-03-18 09:19:07, Mike Kravetz wrote: > On 03/16/2018 03:17 AM, Michal Hocko wrote: > > On Thu 08-03-18 16:27:26, Mike Kravetz wrote: > > > > OK, looks good to me. Hairy but seems to be the easiest way around this. > > Acked-by: Michal Hocko <mhocko@xxxxxxxx> > > > <snip> > >> +/* > >> + * Mask used when checking the page offset value passed in via system > >> + * calls. This value will be converted to a loff_t which is signed. > >> + * Therefore, we want to check the upper PAGE_SHIFT + 1 bits of the > >> + * value. The extra bit (- 1 in the shift value) is to take the sign > >> + * bit into account. > >> + */ > >> +#define PGOFF_LOFFT_MAX (PAGE_MASK << (BITS_PER_LONG - (2 * PAGE_SHIFT) - 1)) > > Thanks Michal, > > However, kbuild found a problem with this definition on certain configs. > Consider a config where, > BITS_PER_LONG = 32 (32bit config) > PAGE_SHIFT = 16 (64K pages) > This results in the negative shift value. > Not something I would not immediately think of, but a valid config. Well, 64K pages on 32b doesn't sound even remotely sane to me but what ever. > The definition has been changed to, > #define PGOFF_LOFFT_MAX \ > (((1UL << (PAGE_SHIFT + 1)) - 1) << (BITS_PER_LONG - (PAGE_SHIFT + 1))) > > as discussed here, > http://lkml.kernel.org/r/432fb2a3-b729-9c3a-7d60-890b8f9b10dd@xxxxxxxxxx This looks more wild but seems correct as well. You can keep my acked-by Thanks! -- Michal Hocko SUSE Labs