On Wed, Apr 21, 2010 at 04:41:38PM +0200, Jan Kiszka wrote: > Gleb Natapov wrote: > > 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. > > Cool, that's now increasing my level of confusion again: :( > > Thought we only wanted to confirm that it's still safe to inject NMIs > when blocked-by-STI is set. Now we hear that it's also safe when MOV SS > is active? That would directly contradict the SDM (at least the version > I have at hand: June 2009). Or did I misunderstand the answer? > No you don't. I was told that software should be prepared to handle NMI after MOV SS. What part of SDM does this contradict? I found nothing in latest SDM. -- 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
