linux-kernel - Re: [PATCH RFC 0/7] KVM: nVMX: enlightened VMCS initial implementation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <fb38c856-9993-026d-c9ba-f82dcc7b4d88@redhat.com>
Date:   Tue, 19 Dec 2017 13:41:58 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     x86@...nel.org,
        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>,
        Roman Kagan <rkagan@...tuozzo.com>,
        linux-kernel@...r.kernel.org, devel@...uxdriverproject.org
Subject: Re: [PATCH RFC 0/7] KVM: nVMX: enlightened VMCS initial
 implementation

On 18/12/2017 18:17, Vitaly Kuznetsov wrote:
> The original author of these patches does no longer work at Red Hat, I
> agreed to take this over and send upstream. Here is his original
> description:
> 
> "Makes KVM implement the enlightened VMCS feature per Hyper-V TLFS 5.0b.
> I've measured about %5 improvement in cost of a nested VM exit (Hyper-V
> enabled Windows Server 2016 nested in KVM)."

Can you try reproducing this and see how much a simple CPUID loop costs in:

* Hyper-V on Hyper-V (with enlightened VMCS, as a proxy for a full
implementation including the clean fields mask)

* Hyper-V on KVM, with and without enlightened VMCS

The latest kvm/queue branch already cut a lot of the cost of a nested VM
exit (from ~22000 to ~14000 clock cycles for KVM on KVM), so we could
also see if Hyper-V needs shadowing of more fields.

> This is just an initial implementation. By leveraging clean fields mask
> we can further improve performance. I'm also interested in implementing
> the other part of the feature: consuming enlightened VMCS when KVM is
> running on top of Hyper-V.

I'm also interested in consuming enlightened VMCS on Hyper-V if that can
provide better performance for KVM on Azure.

Paolo