On Tue, Feb 16, 2010 at 11:37:15AM +0100, Jan Kiszka wrote: > Gleb Natapov wrote: > > On Tue, Feb 16, 2010 at 11:27:07AM +0100, Jan Kiszka wrote: > >> Gleb Natapov wrote: > >>> On Tue, Feb 16, 2010 at 11:14:45AM +0100, Jan Kiszka wrote: > >>>> Gleb Natapov wrote: > >>>>> On Tue, Feb 16, 2010 at 11:04:10AM +0100, Jan Kiszka wrote: > >>>>>> Gleb Natapov wrote: > >>>>>>> On Tue, Feb 16, 2010 at 10:16:12AM +0100, Jan Kiszka wrote: > >>>>>>>> Found while browsing Xen code: While we assume that the STI interrupt > >>>>>>>> shadow also inplies virtual NMI blocking, some processors may have a > >>>>>>>> different opinion (SDM 3: 22.3). To avoid misunderstandings that would > >>>>>>>> cause endless VM entry attempts, translate STI into MOV SS blocking when > >>>>>>>> requesting the NMI window. > >>>>>>>> > >>>>>>> Why not just remove "block by STI" check in vmx_nmi_allowed()? IIRC this > >>>>>>> is documented that on some CPUs STI does not block NMI. > >>>>>>> > >>>>>> Probably because we will stumble and fall on those CPUs that do care. > >>>>>> > >>>>> But this defines behaviour of cpu _we_ emulate. So on _our_ cpu NMI will > >>>>> not be blocked by STI. > >>>> The host CPU decides if it accepts an NMI injections while > >>> Are you sure? I haven't found such check during VMENTRY. > >> I also only find the explicitly stated exclusion of MOV SS blocking vs. > >> NMI injection. If we can rely on this, removing STI blocking from > >> vmx_nmi_allowed should suffice. Or, better, can we get an official > >> confirmation from Intel? > >> > > SDM 2b says about STI instruction: > > The IF flag and the STI and CLI instructions do not prohibit the > > generation of exceptions and NMI interrupts. NMI interrupts (and SMIs) > > may be blocked for one macroinstruction following an STI. > > Yes, it's likely that this is the architectural reason for the delayed > NMI window signaling after STI. Still, we are looking for the > entry-check logic. > Will ask Intel. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
