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Re: [qemu-s390x] [PATCH v8 3/6] s390x/kvm: enable/disable AP instruction

From: Cornelia Huck
Subject: Re: [qemu-s390x] [PATCH v8 3/6] s390x/kvm: enable/disable AP instruction interpretation for guest
Date: Thu, 20 Sep 2018 12:33:19 +0200

On Wed, 19 Sep 2018 10:18:39 +0200
David Hildenbrand <address@hidden> wrote:

> My suggestion, either
> a) Only use KVM_S390_VM_CPU_FEAT_AP to indicate/enable APIE statically
>    for the guest.
> b) Only use KVM_S390_VM_CRYPTO_ENABLE_APIE to indicate/enable APIE
>    dynamically.
> Both things will be simple to implement.
> The difference really is that, with interface a), we will never be able
> to support emulated devices in QEMU (as Christian mentioned, maybe that
> is never the case). Because at the time the CPU model is configured, we
> have no idea about which devices will get added. And we have to make a
> decision (e.g. enable APIE) before creating CPUs and therefore before
> creating AP devices. We will then need most probably a new interface
> that allows us to enable/disable it dynamically.
> With b) however, we have more flexibility. We can defer the decision.

Given that, I think I'd prefer b).

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