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 <[email protected]>
>
<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/[email protected]
--
Mike Kravetz
