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Subject: Re: [PATCH 00/19] KVM: PPC: Book3S HV: add XIVE native exploitation
 mode
To: David Gibson <david@gibson.dropbear.id.au>
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Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

>> With the dual mode, the interrupt mode 
>> is negotiated at CAS time and when merged, the KVM device will be created 
>> at reset. In case of failure, QEMU will abort. 
>>
>> I am not saying it is not possible but we will need some internal 
>> infrastructure to handle dynamically the fall back to userspace
>> emulation.
> 
> Uh.. we do?  I think in all cases we need to make the XICS vs. XIVE
> decision first (i.e. what we present to the guest), then we should
> decide how to implement it (userspace, KVM accelerated, impossible and
> give up).

I am changing things with the addition of KM support for dual mode but 
that might not be the right approach. Let's talk over it when you reach 
the end of the QEMU patchset.

I will keep in mind that we should know exactly what KVM supports
before the machine starts. That is : not to abort QEMU if we can not 
satisfy the interrupt mode chosen at CAS time. It might be possible
to fallback to XIVE emulated mode, I think that is where the problem
is but I haven't looked at it closely.

C.