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 11:04:10AM +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
blocked-by-STI is set, not we. But, of course, we could also translate
STI into MOV SS blocking unconditionally. Whatever is preferred.

Jan

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