Re: [Xen-devel] [PATCH V2] xen: vmx: Use an INT 2 call to process real NMI's instead of self_nmi() in VMEXIT handler

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 15.11.12 at 18:25, Tim Deegan <tim@xxxxxxx> wrote:
> At 16:52 +0000 on 15 Nov (1352998340), Andrew Cooper wrote:
>> It is also possible to get a reentrant NMI if there is a pagefault (or
>> handful of other possible faults) when trying to execute the iret of
>> the NMI itself; NMIs can get re-enabled from the iret of the
>> pagefault, and we take a new NMI before attempting to retry the iret
>> from the original NMI.
> 
> Yes, I hadn't thought of that case.

But what would make a fault happen on that IRET? Oh, yes,
there is one case - the guest having its previous instruction end
exactly at the canonical/non-canonical boundary. But for the
sake of correctness, that's a #GP then. I would suppose this
would better be filtered (manually injecting a #GP into the guest)
than allowed to actually cause a #GP.

Jan


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