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

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Message-ID: <20170711191334.GB3442@potion>
Date:   Tue, 11 Jul 2017 21:13:34 +0200
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Bandan Das <bsd@...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

2017-07-11 14:35-0400, Bandan Das:
> Jim Mattson <jmattson@...gle.com> writes:
> ...
> >>> I can find the definition for an vmexit in case of index >=
> >>> VMFUNC_EPTP_ENTRIES, but not for !vmcs12->eptp_list_address in the SDM.
> >>>
> >>> Can you give me a hint?
> >>
> >> I don't think there is. Since, we are basically emulating eptp switching
> >> for L2, this is a good check to have.
> >
> > There is nothing wrong with a hypervisor using physical page 0 for
> > whatever purpose it likes, including an EPTP list.
> 
> Right, but of all the things, a l1 hypervisor wanting page 0 for a eptp list
> address most likely means it forgot to initialize it. Whatever damage it does will
> still end up with vmfunc vmexit anyway.

Most likely, but not certainly.  I also don't see a to diverge from the
spec here.