On Thu, Aug 03, 2017 at 04:20:45PM +0200, Maxime Villard wrote: > > I was more thinking in terms of a single page in kernel VA, not in user > > VA. That would side step most of the issues with dynamic LDT or having > > to patch up the default LDT on context switches. That said, the latter > > wouldn't be that difficult either, given that we already do that for the > > GDT. > > Mmh, not sure what you mean. If you mean a page that is a kernel page (in the > sense of not having PG_u), then it's a privileged call gate, and we're back > on the first issue (being in kernel mode, with user segment registers, and > interrupts enabled). If you mean a page this a userland page (with PG_u), but > located in the kernel VA range, that's not a good idea: it all of a sudden > makes the map less consistent, and it is more complicated since the upper > levels of the page tree need to have PG_u too.
I was thinking of a page in the kernel VA range that is accessible for userland. I thought we had some of those already for the comm page, but I might be misremember. We can also put it at the top of the user VA range of course, i.e. where the stack used to originate. Joerg
