On Sun, Nov 26, 2017 at 8:24 AM, Dave Hansen <dave.han...@linux.intel.com> wrote: > On 11/26/2017 08:10 AM, Andy Lutomirski wrote: >>> As a side benefit, this shouldn't have magical interactions with the >>> vsyscall page any more. >>> >>> Are there cases that this would get wrong? >>> >> Quick ping: did this get lost? > > It does drop a warning that the other version of the code has, but > that's pretty minor. > > Basically, we need two checks: > > pgd_userspace_access() (aka _PAGE_USER) and > pgdp_maps_userspace() > > The original code does pgd_userspace_access() in a top-level if and then > the pgdp_maps_userspace() checks at the second level. I think you are > basically suggesting that we flip that. > > Logically, I'm sure we can make it work. It's just a matter of needing > to look at other things first. > > BTW, this comment is, I think incorrect: > >> if (pgdp_maps_userspace(pgdp)) { > ... >> } else { >> /* >> * We can get here due to vmalloc, a vmalloc fault, memory >> hot-add, or initial setup >> * of kernelmode page tables. Regardless of which particular code >> path we're in, >> * these mappings should not be automatically propagated to the >> usermode tables. >> */ > > Since we pre-populated the entire kernel area's PGDs, I don't think > we'll ever have a valid reason to be doing a set_pgd() again on the > kernel area.
Right, forgot about that. So it's just initial setup, then.