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

From Radim Krčmář <rkrcmar@redhat.com>
Newsgroups linux.kernel
Subject Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor
Date 2017-07-12 15:50 +0200
Message-ID <u2qbD-pT-5@gated-at.bofh.it> (permalink)
References (5 earlier) <u28eK-5Oe-3@gated-at.bofh.it> <u28Rr-6kH-1@gated-at.bofh.it> <u29aO-6ru-31@gated-at.bofh.it> <u29Xc-6WM-17@gated-at.bofh.it> <u2agx-73x-1@gated-at.bofh.it>
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2017-07-11 16:45-0400, Bandan Das:
> Radim Krčmář <rkrcmar@redhat.com> writes:
> 
> > 2017-07-11 15:38-0400, Bandan Das:
> >> Radim Krčmář <rkrcmar@redhat.com> writes:
> >> 
> >> > 2017-07-11 14:35-0400, Bandan Das:
> >> >> Jim Mattson <jmattson@google.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. :)
> 
> 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.

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Thread

[PATCH v4 0/3] Expose VMFUNC to the nested hypervisor Bandan Das <bsd@redhat.com> - 2017-07-10 23:00 +0200
  [PATCH v4 2/3] KVM: nVMX: Enable VMFUNC for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-10 23:00 +0200
  [PATCH v4 1/3] KVM: vmx: Enable VMFUNCs Bandan Das <bsd@redhat.com> - 2017-07-10 23:00 +0200
  [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-10 23:00 +0200
    Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor David Hildenbrand <david@redhat.com> - 2017-07-11 10:00 +0200
      Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Paolo Bonzini <pbonzini@redhat.com> - 2017-07-11 10:50 +0200
      Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-11 16:00 +0200
        Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-11 20:10 +0200
          Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-11 21:20 +0200
            Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-11 21:40 +0200
      Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-11 20:00 +0200
        Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-11 20:30 +0200
          Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-11 21:40 +0200
            Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-11 22:00 +0200
              Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-11 22:30 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-11 22:40 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-11 22:50 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-11 23:10 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-12 15:30 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-12 20:20 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-12 21:20 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-17 20:00 +0200
        Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Jim Mattson <jmattson@google.com> - 2017-07-11 20:30 +0200
          Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-11 20:40 +0200
            Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-11 21:20 +0200
              Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-11 21:40 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-11 22:30 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-11 22:50 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor Radim Krčmář <rkrcmar@redhat.com> - 2017-07-12 15:50 +0200
                Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-12 20:10 +0200
        Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1  hypervisor David Hildenbrand <david@redhat.com> - 2017-07-13 17:50 +0200
          Re: [PATCH v4 3/3] KVM: nVMX: Emulate EPTP switching for the L1 hypervisor Bandan Das <bsd@redhat.com> - 2017-07-13 19:10 +0200

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