On Mon, Nov 13, 2017 at 10:05 AM, Tobin C. Harding <m...@tobin.cc> wrote: > On Mon, Nov 13, 2017 at 06:37:28AM +0300, Kirill A. Shutemov wrote: >> On Mon, Nov 13, 2017 at 10:06:46AM +1100, Tobin C. Harding wrote: >> > On Sun, Nov 12, 2017 at 02:10:07AM +0300, Kirill A. Shutemov wrote: ... >> > >> > Thanks for the link. So it looks like we need to refactor the kernel >> > address regular expression into a function that takes into account the >> > machine architecture and the number of page table levels. We will need >> > to add this to the false positive checks also. >> > >> > > Not sure if we care. It won't work too for other 64-bit architectrues >> > > that >> > > have more than 256TB of virtual address space. >> > >> > Is this because of the virtual memory map? >> >> On x86 direct mapping is the nearest thing we have to userspace. >> >> > Did you mean 512TB? >> >> No, I mean 256TB. >> >> You have all kernel memory in the range from 0xffff000000000000 to >> 0xffffffffffffffff if you have 256 TB of virtual address space. If you >> hvae more, some thing might be ouside the range. > > Doesn't 4-level paging already limit a system to 64TB of memory? So any > system better equipped than this will use 5-level paging right? If I am > totally talking rubbish please ignore, I'm appreciative that you pointed > out the limitation already. Perhaps we can add a comment to the script > > # Script may miss some addresses on machines with more than 256TB of > # memory.
I think the 256TB is wrt *virtual* address space not physical RAM. Also, IMHO, the script should 'transparently' take into account the # of paging levels (instead of the user needing to pass a parameter). IOW it should be able to detect the same (say, from the .config file) and act accordingly - in the sense, the regex's and associated logic would accordingly differ.
