On Thu, Mar 19, 2020 at 12:26 PM Joerg Roedel <jroedel@xxxxxxx> wrote: > > On Thu, Mar 19, 2020 at 11:40:39AM -0700, Andy Lutomirski wrote: > > > Nope. A nested NMI will reset the interrupted NMI's return frame to > > cause it to run again when it's done. I don't think this will have > > any real interaction with #VC. There's no longjmp() here. > > Ahh, so I misunderstood that part, in this case your proposal of sending > the NMI-complete message right at the beginning of do_nmi() should work > just fine. I will test this and see how it works out. > > > I certainly *like* preventing nesting, but I don't think we really > > want a whole alternate NMI path just for a couple of messed-up AMD > > generations. And the TF trick is not so pretty either. > > Indeed, if it could be avoided, it should. > > > > > > > This causes us to pop the NMI frame off the stack. Assuming the NMI > > > > restart logic is invoked (which is maybe impossible?), we get #DB, > > > > which presumably is actually delivered. And we end up on the #DB > > > > stack, which might already have been in use, so we have a potential > > > > increase in nesting. Also, #DB may be called from an unexpected > > > > context. > > > > > > An SEV-ES hypervisor is required to intercept #DB, which means that the > > > #DB exception actually ends up being a #VC exception. So it will not end > > > up on the #DB stack. > > > > With your patch set, #DB doesn't seem to end up on the #DB stack either. > > Right, it does not use the #DB stack or shift-ist stuff. Maybe it > should, is this needed for anything else than making entry code > debugable by kgdb? AIUI the shift-ist stuff is because we aren't very good about the way that we handle tracing right now, and that can cause a limited degree of recursion. #DB uses IST for historical reasons that don't necessarily make sense. Right now, we need it for only one reason: the MOV SS issue. IIRC this isn't actually triggerable without debugging enabled -- MOV SS with no breakpoint but TF on doesn't seem to malfunction quite as badly. --Andy > > Regards, > > Joerg _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
