On Thu, Jul 23, 2015 at 2:35 PM, Linus Torvalds <torva...@linux-foundation.org> wrote: > On Thu, Jul 23, 2015 at 2:20 PM, Peter Zijlstra <pet...@infradead.org> wrote: >> >> So the NMI could trigger userspace debug register faults, and simply >> disabling them would make the whole debug register thing entirely >> unreliable. > > We could easily set something to re-enable them for when we actually > return to user space. I'd be ok with just setting the > _TIF_USER_WORK_MASK. > > But even that should not be a requirement for the basic stability and > core integrity of the kernel. Not like the current horrid mess with > NMI nesting and ESP fixing etc. > > And realistically, nobody will ever even notice. So the whole "ok, we > can use _TIF_USER_WORK_MASK to re-enable dr7" is a tiny tiny detail > that is more like cleaning up things, not a core issue. >
Or we just re-enable them on the way out of NMI (i.e. the very last thing we do in the NMI handler). I don't want to break regular userspace gdb when perf is running. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
