linux-kernel - Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor

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Date:   Wed, 12 Jul 2017 14:04:08 -0400
From:   Bandan Das <bsd@...hat.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     Jim Mattson <jmattson@...gle.com>,
        David Hildenbrand <david@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor

Radim Krčmář <rkrcmar@...hat.com> writes:
...
>> > Thanks, we're not here to judge the guest, but to provide a bare-metal
>> > experience. :)
>> 
>> There are certain cases where do. For example, when L2 instruction emulation
>> fails we decide to kill L2 instead of injecting the error to L1 and let it handle
>> that. Anyway, that's a different topic, I was just trying to point out there
>> are cases kvm does a somewhat policy decision...
>
> Emulation failure is a KVM bug and we are too lazy to implement the
> bare-metal behavior correctly, but avoiding the EPTP list bug is
> actually easier than introducing it.  You can make KVM simpler and
> improve bare-metal emulation at the same time.

We are just talking past each other here trying to impose point of views.
Checking for 0 makes KVM simpler. As I said before, a 0 list_address means
that the hypervisor forgot to initialize it. Feel free to show me examples
where the hypervisor does indeed use a 0 address for eptp list address or
anything vm specific. You disagreed and I am fine with it.