From mboxrd@z Thu Jan  1 00:00:00 1970
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [RFC 0/6] Enlightened VMCS support for KVM on Hyper-V
Date: Tue, 16 Jan 2018 13:05:26 +0100
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References: <20180115173105.31845-1-vkuznets@redhat.com>
        <CANRm+Cza82KuvEQQi=2Zio2u0EHm1kfPfr=aOhoLdra+fpB2Wg@mail.gmail.com>
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Cc: kvm <kvm@vger.kernel.org>,
        "the arch\/x86 maintainers" <x86@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "Michael Kelley \(EOSG\)" <Michael.H.Kelley@microsoft.com>,
        Mohammed Gamal <mmorsy@redhat.com>,
        Cathy Avery <cavery@redhat.com>, Bandan Das <bsd@redhat.com>,
        linux-kernel@vger.kernel.org
To: Wanpeng Li <kernellwp@gmail.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <CANRm+Cza82KuvEQQi=2Zio2u0EHm1kfPfr=aOhoLdra+fpB2Wg@mail.gmail.com>
        (Wanpeng Li's message of "Tue, 16 Jan 2018 09:21:04 +0800")
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Wanpeng Li <kernellwp@gmail.com> writes:

> 2018-01-16 1:30 GMT+08:00 Vitaly Kuznetsov <vkuznets@redhat.com>:
>> Early RFC. I'll refer to this patchset in my DevConf/FOSDEM
>> presentations.
>>
>> When running nested KVM on Hyper-V it's possible to use so called
>> 'Enlightened VMCS' and do normal memory reads/writes instead of
>> doing VMWRITE/VMREAD instructions. Tests show that this speeds up
>> tight CPUID loop almost 3 times:
>>
>> Before:
>> ./cpuid_tight
>> 20459
>>
>> After:
>> ./cpuid_tight
>> 7698
>
> Maybe you can apply a similar idea to kvm nested on kvm.
>

Yes we can. Basically, that would mean directly accessing 'struct
vmcs12' from L1 hypervisor.

-- 
  Vitaly