On Wed, Apr 21, 2010 at 04:17:03PM +0200, Jan Kiszka wrote: > Gleb Natapov wrote: > > 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. > > > > Just remembered that there was some open topic... Did your ask? Any answer? > I did and got answer last week :) The answer is that NMI is blocked only if GUEST_INTR_STATE_NMI flag is set. MOV SS and STI shouldn't block NMI, so vmx_nmi_allowed() should check only GUEST_INTR_STATE_NMI flag. -- 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
