linux-kernel - Re: [PATCH v2 3/7] KVM: nVMX: Ignore 'hv_clean_fields' data when eVMCS data is copied in vmx_get_nested

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Date:   Mon, 24 May 2021 15:58:49 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v2 3/7] KVM: nVMX: Ignore 'hv_clean_fields' data when
 eVMCS data is copied in vmx_get_nested_state()

On 24/05/21 15:01, Vitaly Kuznetsov wrote:
> With 'need_vmcs12_to_shadow_sync', we treat eVMCS as shadow VMCS which
> happens to shadow all fields and while it may not be the most optimal
> solution, it is at least easy to comprehend. We can try drafting
> something up instead, maybe it will also be good but honestly I'm afraid
> of incompatible changes in KVM_GET_NESTED_STATE/KVM_SET_NESTED_STATE, we
> can ask Paolo's opinion on that.

Yes, it's much easier to understand it if the eVMCS is essentially a 
memory-backed shadow VMCS, than if it's really the vmcs12 format.  I 
understand that it's bound to be a little slower, but at least the two 
formats are not all over the place.

Paolo