On Fri, 12 Sep 2014, Thomas Gleixner wrote: > On Thu, 11 Sep 2014, Dave Hansen wrote: > > Well, we use it to figure out whether we _potentially_ need to tear down > > an VM_MPX-flagged area. There's no guarantee that there will be one. > > So what you are saying is, that if user space sets the pointer to NULL > via the unregister prctl, kernel can safely ignore vmas which have the > VM_MPX flag set. I really can't follow that logic. > > mmap_mpx(); > prctl(enable mpx); > do lots of crap which uses mpx; > prctl(disable mpx); > > So after that point the previous use of MPX is irrelevant, just > because we set a pointer to NULL? Does it just look like crap because > I do not get the big picture how all of this is supposed to work? do_bounds() will happily map new BTs no matter whether the prctl was invoked or not. So what's the value of the prctl at all? The mapping is flagged VM_MPX. Why is this not sufficient? Thanks, tglx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>