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Subject: Re: [PATCH RFC 2/3] x86/kvm/hyper-v: move VMX controls sanitization
 out of nested_enable_evmcs()
To:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     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>
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From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <437c2710-7148-a675-8945-71dc7a90f7dd@redhat.com>
Date:   Mon, 27 Jan 2020 18:53:40 +0100
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On 27/01/20 16:38, Vitaly Kuznetsov wrote:
>>> If there are no objections and if we still think it would be beneficial
>>> to minimize the list of controls we filter out (and not go with the full
>>> set like my RFC suggests), I'll prepare v2. (v1, actually, this was RFC).
>> 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...
> 

Indeed.  The place you used in the RFC is the best we can do, I am afraid.

Paolo