Messages in this thread | | | Date | Thu, 19 Mar 2020 20:26:54 +0100 | From | Joerg Roedel <> | Subject | Re: [PATCH 70/70] x86/sev-es: Add NMI state tracking |
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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
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