kernel-packages team mailing list archive

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

Cool, so we need to get that pulled into stable. Sorry for being unclear
before. Yes, my kernel just had the patch from bisection reverted. The
kernel Seth made had the fix for that on top.

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https://bugs.launchpad.net/bugs/1278531

Title:
  nested kvm fails with trusty and upstream kernels

Status in “linux” package in Ubuntu:
  Confirmed

Bug description:
  First: the 3.2 precise kernel handled nested qemu very well.  As of
  saucy it has declined.

  In a host with saucy kernel (even on precise userspace), attempts to
  do nested kvm result in a hung kvm (inside the guest - host proceeds
  ok) taking 100%cpu.

  In a host with trusty kernel (even on precise userspace), nested kvm
  fails get past grub.  I have two screenshots, one resulting from
  attempting to boot from a precise mini-iso, another from attempting to
  boot a cloud image at:  http://cloud-images.ubuntu.com/quantal/current
  /quantal-server-cloudimg-amd64-disk1.img.  (If you convert that image
  to raw, it fails the same way).

  On the host, I see the following in /var/log/kern.log: kvm: zapping
  shadow pages for mmio generation wraparound

  I've reproduced this both on (a) a intel based vostro laptop - with
  separate installs of precise and saucy (with ubuntu precise, saucy,
  trust, upstream kernels), (b) an intel based server with precise
  userspace and saucy and trusty kernels;  and (c) an intel laptop
  running full uptodate trusty.

  As nested qemu worked will in the previous LTS, I think it is
  important to have it working in 14.04 LTS.

  ============= Original description ================
  I have a precise host with saucy ubuntu kernel installed.  I installed two VMs there, a saucy and a trusty guest.

  In the saucy guest, non-accelerated qemu works fine, but accelerated
  kvm hangs the first-level saucy guest completely, and pins it at 200%
  cpu usage:

     qemu-system-x86 --enable-kvm -monitor stdio -vnc :1

  On the trusty guest it works just fine.

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