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. 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 -- Mike Kravetz
