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? Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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
