0000000000000000 - 00007fffffffffff (=47bits) user space, different per mm
hole caused by [48:63] sign extension
ffff800000000000 - ffff80ffffffffff (=40bits) guard hole
0000000000000000 - 00007fffffffffff (=47bits) user space, different per mm
hole caused by [48:63] sign extension
ffff800000000000 - ffff80ffffffffff (=40bits) guard hole