linux-kernel - Re: [PATCH v2 6/6] KVM: nVMX: optimize prepare_vmcs02{,

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Date:   Wed, 25 Jul 2018 16:13:12 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org,
        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>,
        Mohammed Gamal <mmorsy@...hat.com>,
        Cathy Avery <cavery@...hat.com>, linux-kernel@...r.kernel.org,
        Jim Mattson <jmattson@...gle.com>,
        Liran Alon <liran.alon@...cle.com>
Subject: Re: [PATCH v2 6/6] KVM: nVMX: optimize prepare_vmcs02{,_full} for Enlightened VMCS case

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

> On 25/07/2018 15:26, Vitaly Kuznetsov wrote:
>
>> The other place where we set dirty_vmcs12 is the newly introduced
>> vmx_set_nested_state() but I think I'm going to add support for eVMCS
>> there later and just return something like -ENOTSUPP for now. Too many
>> people work on nested simultaneously :-)
>
> Hmm, I think that means you have to put the clean fields in the
> vmx_nested struct.  Then it's really easy in vmx_set_nested_state to
> clear all the clean bits.  Touching memory in vmx_set_nested_state is...
> *puts on sunglasses* a touchy subject (see comment in kvm/queue's
> enter_vmx_non_root_mode).
>

Not only clean fields, in case we can't touch memory in
vmx_set_nested_state I guess we'll need to cache the whole eVMCS, just
like we save cached_shadow_vmcs12. Anyway, let's eat the elephant one
bite at a time :-)

-- 
  Vitaly