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

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Message-ID: <20170711202227.GC3442@potion>
Date:   Tue, 11 Jul 2017 22:22:27 +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 15:38-0400, Bandan Das:
> Radim Krčmář <rkrcmar@...hat.com> writes:
> 
> > 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.
> 
> Actually, this is a specific case where I would like to diverge from the spec.
> But then again, it's L1 shooting itself in the foot and this would be a rarely
> used code path, so, I am fine removing it.

Thanks, we're not here to judge the guest, but to provide a bare-metal
experience. :)