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? Regards, Joerg
