Re: [PATCH] KVM: VMX: Translate interrupt shadow when waiting on NMI window

[Jan Kiszka <jan.kiszka@siemens.com>]

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?

Jan

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