[Bug 64801] New: Nested Virtualisation with KVM on Intel and AMD processors: L2 unreachable

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=64801

            Bug ID: 64801
           Summary: Nested Virtualisation with KVM on Intel and AMD
                    processors: L2 unreachable
           Product: Virtualization
           Version: unspecified
    Kernel Version: 3.12
          Hardware: x86-64
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: kvm
          Assignee: virtualization_kvm@kernel-bugs.osdl.org
          Reporter: 2005@kuarepoti-dju.net
        Regression: No

With the recent kernel version(s) it seems to be impossible to reach an L2
guest. The issues sometimes even render the L0 machine unusable, and hence
could be considered relevant to system security.

On three machines, the combination of KVM 1.2 and Linux 3.12 produces the
following results when invoking the L2 VM:

* Intel Core i5 680: register dump
* Intel Core i7 M620: "nested_vmx_run: VMCS MSR_{LOAD,STORE} unsupported"
* AMD Athlon X2 3800+: "skip emulated instructions" messages thrown over all
host ttys

On another machine, AMD Athlon II X2 240e which runs Linux 3.2.0 as host with
KVM 1.1 and Linux 3.9.0 as guests, L2 can be reached. Booting the test setup
from above with Linux 3.12 on all levels for comparing the results was not yet
possible. The test setup consists of a minimal textmode VM which nests itself
twice and contains some extra configuration for L0 for hardware support. Both
SMP and single-core configurations seem to show the same behaviour.

Kernel 3.12 host (L0) minimal configuration; may need tweaks depending on the
hardware in use:

http://serviceplatform.org/cgi-bin/gitweb.cgi?p=space-cloud;a=blob_plain;f=nestedcloud/kernel-boot/customkernel/nestedcloud.hostkernel.config;hb=master

Kernel 3.12 guest (L1+L2) minimal configuration:

https://gitorious.org/recvirt/recvirt/raw/2d4aeef70e53df7a2199256550515cd3bdbd4ecd:recvirt-basevm/kernel/recvirt.kvmkernel-smpfull.config

Complete L0 test image (~800 MB) with extlinux as bootloader; may need root=
and kvm_intel.nested=1 parameters, or PROMPT 1 in extlinux.conf; login is root,
password is demo:

http://141.76.41.201/recvirt/

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