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Date:   Mon, 27 Jan 2020 10:17:27 -0800
From:   Sean Christopherson <sean.j.christopherson@intel.com>
To:     Vitaly Kuznetsov <vkuznets@redhat.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org,
        Jim Mattson <jmattson@google.com>,
        linux-kernel@vger.kernel.org, Liran Alon <liran.alon@oracle.com>,
        Roman Kagan <rkagan@virtuozzo.com>
Subject: Re: [PATCH RFC 2/3] x86/kvm/hyper-v: move VMX controls sanitization
 out of nested_enable_evmcs()
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On Mon, Jan 27, 2020 at 04:38:27PM +0100, Vitaly Kuznetsov wrote:
> Sean Christopherson <sean.j.christopherson@intel.com> writes:
> > One last idea, can we keep the MSR filtering as is and add the hack in
> > vmx_restore_control_msr()?  That way the (userspace) host and guest see
> > the same values when reading the affected MSRs, and eVMCS wouldn't need
> > it's own hook to do consistency checks.
> 
> Yes but (if I'm not mistaken) we'll have then to keep the filtering we
> currently do in nested_enable_evmcs(): if userspace doesn't do
> KVM_SET_MSR for VMX MSRs (QEMU<4.2) then the filtering in
> vmx_restore_control_msr() won't happen and the guest will see the
> unfiltered set of controls...

Ya, my thought was to add this on top of the nested_enable_evmcs() code.