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From:   Vitaly Kuznetsov <vkuznets@redhat.com>
To:     Paolo Bonzini <pbonzini@redhat.com>,
        Jim Mattson <jmattson@google.com>
Cc:     Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Roman Kagan <rkagan@virtuozzo.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>,
        LKML <linux-kernel@vger.kernel.org>,
        Liran Alon <liran.alon@oracle.com>,
        kvm list <kvm@vger.kernel.org>
Subject: Re: [PATCH v6 06/13] KVM: nVMX: optimize prepare_vmcs02{,_full} for Enlightened VMCS case
In-Reply-To: <173cc977-58fd-9431-6199-c2eb8e898f7c@redhat.com>
References: <20181016165011.6607-1-vkuznets@redhat.com> <20181016165011.6607-7-vkuznets@redhat.com> <2064be05-4286-e3d5-cd22-13fd957b7003@redhat.com> <8736t4sk8w.fsf@vitty.brq.redhat.com> <0ff3acb0-1d20-cbb0-5f40-887d9db93d9e@redhat.com> <CALMp9eTtSuguXb=gCWKL9ZKWy5kUve0SNY1Toduf8x2Qn=1s9Q@mail.gmail.com> <173cc977-58fd-9431-6199-c2eb8e898f7c@redhat.com>
Date:   Thu, 18 Oct 2018 13:14:38 +0200
Message-ID: <87sh13qzfl.fsf@vitty.brq.redhat.com>
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Paolo Bonzini <pbonzini@redhat.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