linux-kernel - Re: [RFC 0/6] Enlightened VMCS support for KVM on Hyper-V

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Message-ID: <87inc2huux.fsf@vitty.brq.redhat.com>
Date:   Tue, 16 Jan 2018 13:05:26 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     kvm <kvm@...r.kernel.org>,
        "the arch\/x86 maintainers" <x86@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "Michael Kelley \(EOSG\)" <Michael.H.Kelley@...rosoft.com>,
        Mohammed Gamal <mmorsy@...hat.com>,
        Cathy Avery <cavery@...hat.com>, Bandan Das <bsd@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 0/6] Enlightened VMCS support for KVM on Hyper-V

Wanpeng Li <kernellwp@...il.com> writes:

> 2018-01-16 1:30 GMT+08:00 Vitaly Kuznetsov <vkuznets@...hat.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