On Wed, Dec 13, 2017 at 12:44 AM, Damian Tometzki <damian.tometzki@xxxxxxxxxx> wrote: > Hello all, > > i have a short question: > > How are the bits (in brackets) calculated in the virtual memory map ? > > for example the first line (=47 bits) > > Virtual memory map with 4 level page tables: > > 0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm > hole caused by [47:63] sign extension > ffff800000000000 - ffff87ffffffffff (=43 bits) guard hole, reserved for hypervisor > Presently for x86-64 kernel uses 4-level paging. Out of 64bit only 48 bit is enabled (Which boils down to Terabyte of address space). For case where getpagesize() is 4K the breakup is :- CR3 -> Global(9 bits) -> Upper(9 bits) -> Middle(9 bits) -> Page table(9 bits) -> [12 bits for page or 4096 bytes] = (48 bits) Thanks _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
