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From: Pavel Fedin <p.fedin@samsung.com>
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Date: Mon, 21 Dec 2015 16:28:12 +0300
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Subject: Re: [Qemu-devel] [PATCH v4 5/5] kvm/x86: Hyper-V kvm exit
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To: asmetanin@virtuozzo.com, 'Roman Kagan' <rkagan@virtuozzo.com>, 'Peter Hornyack' <peterhornyack@google.com>, 'Paolo Bonzini' <pbonzini@redhat.com>, 'kvm list' <kvm@vger.kernel.org>, "'Denis V. Lunev'" <den@openvz.org>, 'Gleb Natapov' <gleb@kernel.org>, qemu-devel@nongnu.org

 Hello!

> Yes, we can use  KVM_EXIT_REG_IO/MSR_IO for Hyper-V SynIC MSRS's changes
> and can even use only one MSR value . So union inside struct
> kvm_hyperv_exit is excessive.
> 
> But we still need Vcpu exit to handle VMBus hypercalls by QEMU to
> emulate VMBus devices inside QEMU.
> 
> And currently we are going to extend struct kvm_hyperv_exit
> to store Hyper-V VMBus hypercall parameters.

 Hm... Hypercalls, you say?
 We already have KVM_EXIT_HYPERCALL. Documentation says it's currently unused. Is it a leftover from ia64 KVM? Could we reuse it for
the purpose?

> but could we replace Hyper-V VMBus hypercall and it's parameters
> by KVM_EXIT_REG_IO/MSR_IO too?

 It depends. Can i read about these hypercalls somewhere? Is there any documentation?

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia