linux-kernel - Re: [PATCH v6 06/13] KVM: nVMX: optimize prepare_vmcs02{,

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Message-ID: <87sh13qzfl.fsf@vitty.brq.redhat.com>
Date:   Thu, 18 Oct 2018 13:14:38 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Roman Kagan <rkagan@...tuozzo.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>,
        LKML <linux-kernel@...r.kernel.org>,
        Liran Alon <liran.alon@...cle.com>,
        kvm list <kvm@...r.kernel.org>
Subject: Re: [PATCH v6 06/13] KVM: nVMX: optimize prepare_vmcs02{,_full} for Enlightened VMCS case

Paolo Bonzini <pbonzini@...hat.com> writes:

> On 17/10/2018 19:08, Jim Mattson wrote:
>> I believe that ESXi reads GUEST_CS_AR_BYTES on every VM-exit to
>> determine code size.
>
> Which makes me wonder, maybe we should add GUEST_SS_AR_BYTES which is
> where the CPL lives.  But then your tests from last year didn't find it.
>

Hyper-V does read GUEST_SS_AR_BYTES. Way less frequent than
GUEST_CS_AR_BYTES but still.

Based on that my suggestion would be to shadow GUEST_SS_AR_BYTES, keep
GUEST_SS_AR_BYTES and unshadow the rest (GUEST_ES_BASE,
GUEST_CS_SELECTOR, GUEST_CS_LIMIT, GUEST_CS_BASE). I can do this as a
separate patch as I see this series is already in kvm/queue.

-- 
Vitaly