On Mon, Aug 20, 2018 at 03:27:52PM -0700, Linus Torvalds wrote: > On Mon, Aug 20, 2018 at 3:02 PM Woodhouse, David <dwmw@xxxxxxxxxxxx> wrote: > > > > It's the *kernel* we don't want being able to access those pages, > > because of the multitude of unfixable cache load gadgets. > > Ahh. > > I guess the proof is in the pudding. Did somebody try to forward-port > that patch set and see what the performance is like? > > It used to be just 500 LOC. Was that because they took horrible > shortcuts? Are the performance numbers for the 32-bit case that > already had the kmap() overhead? The last version I worked on was a bit before Meltdown was public: https://lkml.org/lkml/2017/9/7/445 The overhead was a lot, but Dave Hansen gave some ideas about how to speed things up in this thread: https://lkml.org/lkml/2017/9/20/828 Since meltdown hit, I haven't worked seriously on understand and implementing his suggestions, in part because it wasn't clear to me what pieces of the infrastructure we might be able to re-use. Someone who knows more about mm/ might be able to suggest an approach, though. Tycho
