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Date: Wed, 17 Apr 2013 13:12:37 +0100
From: "Jan Beulich" <JBeulich@suse.com>
To: "Michael S. Tsirkin" <mst@redhat.com>, "Victor Miasnikov" <vvm@tut.by>
Cc: <olaf@aepfle.de>, <bp@alien8.de>, <apw@canonical.com>, <x86@kernel.org>,
        <tglx@linutronix.de>, <devel@linuxdriverproject.org>,
        <gregkh@linuxfoundation.org>, "K. Y. Srinivasan" <kys@microsoft.com>,
        <jasowang@redhat.com>, <linux-kernel@vger.kernel.org>, <hpa@zytor.com>
Subject: Re: KVM  "Hyper-V emulation"   -- this can be related "Linux
 on Hyper-V" ? Or  "KVM emulates Hyper-V" as  "Hyper-V emulates
 Hyper-V" ? Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of
 Hyper-V
References: <1359940910-32114-1-git-send-email-kys@microsoft.com>
 <1359940959-32168-1-git-send-email-kys@microsoft.com>
 <1359940959-32168-2-git-send-email-kys@microsoft.com>
 <20130417070616.GA4487@redhat.com>
 <39D7C3658A5B4979A3F025E1D944E743@local.st.by>
 <20130417101617.GF3881@redhat.com>
In-Reply-To: <20130417101617.GF3881@redhat.com>
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>>> On 17.04.13 at 12:16, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> If the hypervisor says it's Hyper-V, that's because it wants
> guests to use Hyper-V. I don't see why is guest second-guessing
> this a good idea.

There are two reasons here: For one, when the hypervisor is not
Hyper-V, but is providing some Hyper-V emulation, that's intended
for Windows guests to use, not e.g. Linux ones, especially when
such guests could use the native hypervisor interface with much
greater benefit.

And second, there reportedly are features of (newer?) Hyper-V
that some emulation may not provide, but that are also not easily
detectable.

Jan