| 2014-02-24 16:43:23 |
Serge Hallyn |
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. |
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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