nSVM: Booting L2 results in L1 hang and a "skip_emulated_instruction"

[Kashyap Chamarthy <kchamart@redhat.com>]

Hi, 

This was tested with kernel-3.19.0-1.fc22) and QEMU (qemu-2.2.0-5.fc22)
on L0 & L1.


Description
-----------

Inside L1, boot a nested KVM guest (L2) . Instead of a full blown
guest, let's use `qemu-sanity-check` with KVM:

    $ qemu-sanity-check --accel=kvm

Wwich gives you this CLI (run from a different shell), that confirms
that the L2 guest is indeed running on KVM (and not TCG):

  $ ps -ef | grep -i qemu
  root       763   762 35 11:49 ttyS0    00:00:00 qemu-system-x86_64 -nographic -nodefconfig -nodefaults -machine accel=kvm -no-reboot -serial file:/tmp/tmp.rl3naPaCkZ.out -kernel /boot/vmlinuz-3.19.0-1.fc21.x86_64 -initrd /usr/lib64/qemu-sanity-check/initrd -append console=ttyS0 oops=panic panic=-1


Which results in:

  (a) L1 (guest hypervisor) completely hangs and is unresponsive. But
      when I query libvirt, (`virsh list`) the guest is still reported
      as 'running'

  (b) On L0, I notice a ton of these messages:

        skip_emulated_instruction: ip 0xffec next 0xffffffff8105e964


I can get `dmesg`, `dmidecode` , `x86info -a` on L0 and L1 if it helps
in narrowing down the issue.


Related bug and reproducer details
----------------------------------


https://bugzilla.redhat.com/show_bug.cgi?id=1191665 --  Nested KVM with
AMD: L2 (nested guest) fails with "divide error: 0000 [#1] SMP"




-- 
/kashyap