Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 28 Feb 2018 19:48:22 +0300
From:   Roman Kagan <rkagan@virtuozzo.com>
To:     Vitaly Kuznetsov <vkuznets@redhat.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>,
        Andrey Smetanin <asmetanin@virtuozzo.com>,
        "Denis V . Lunev" <den@openvz.org>
Subject: Re: [PATCH 1/3] x86/kvm/hyper-v: add reenlightenment MSRs support
Message-ID: <20180228164822.GA12531@rkaganb.sw.ru>
Mail-Followup-To: Roman Kagan <rkagan@virtuozzo.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>,
        Andrey Smetanin <asmetanin@virtuozzo.com>,
        "Denis V . Lunev" <den@openvz.org>
References: <20180228134401.6544-1-vkuznets@redhat.com>
 <20180228134401.6544-2-vkuznets@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20180228134401.6544-2-vkuznets@redhat.com>
User-Agent: Mutt/1.9.2 (2017-12-15)
Received-SPF: None (protection.outlook.com: virtuozzo.com does not designate
 permitted sender hosts)
SpamDiagnosticOutput: 1:22
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Feb 2018 16:48:26.0217
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: 2bfd4d8a-b4b4-4ea8-7204-08d57ecb1683
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 0bc7f26d-0264-416e-a6fc-8352af79c58f
X-MS-Exchange-Transport-CrossTenantHeadersStamped: HE1PR0801MB1980
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Feb 28, 2018 at 02:43:59PM +0100, Vitaly Kuznetsov wrote:
> Nested Hyper-V/Windows guest running on top of KVM will use TSC page
> clocksource in two cases:
> - L0 exposes invariant TSC (CPUID.80000007H:EDX[8]).
> - L0 provides Hyper-V Reenlightenment support (CPUID.40000003H:EAX[13]).
> 
> Exposing invariant TSC effectively blocks migration to hosts with different
> TSC frequencies,

I wonder if TSC scaling on the destination host doesn't allow to relax
this requirement?

> providing reenlightenment support will be needed when we
> start migrating nested workloads.
> 
> Implement rudimentary support for reenlightenment MSRs. For now, these are
> just read/write MSRs with no effect.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  4 ++++
>  arch/x86/kvm/hyperv.c           | 21 +++++++++++++++++++++
>  arch/x86/kvm/x86.c              | 12 +++++++++++-
>  3 files changed, 36 insertions(+), 1 deletion(-)

Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>