[Qemu-devel] [Bug 1243287] Re: [KVM/QEMU][ARM][SAUCY] fails to boot cloud-image due to host kvm fail

[Peter Maydell]

(1) If you are trying to mmap /dev/mem then you are going to be
accessing physical addresses. This is obviously totally board specific.
In particular the memory layout between a Midway system and a KVM
virtual machine is likely to be different (you don't say what QEMU
configuration you're using) so it is unsurprising that looking at
/dev/mem address zero gives different effects between the host and the
VM. If dmidecode wants to access physical address space it needs to be
aware of the physical memory layout of every board it might run on (and
that is an enormous range of systems for ARM).

(2) The guest kernel has sufficient privilege to cause kvm to exit (the
easiest way it can do this is to do something that KVM doesn't support,
such as trying to access emulated devices via LDM/STM or some other
"complex" instruction). If you let your guest userspace open /dev/mem it
has equivalent privilege and can do the same thing (again, by trying LDM
on device MMIO space)

(3) My kernel sources don't have any references to CONFIG_STRICT_MEM,
and the only two google hits are references back to this bug report, so
I'm not sure what this is.

My best guess is that there are two underlying bugs here:
a. CONFIG_STRICT_MEM (whatever that is) either doesn't work with ARM or doesn't 
work with KVM or doesn't work with KVM/ARM
b. dmidecode is making bad assumptions about the physical memory layout of the 
machine it is running on and needs to be fixed somehow (what does it think is 
the actual data it is copying out of physical memory??)

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https://bugs.launchpad.net/bugs/1243287

Title:
  [KVM/QEMU][ARM][SAUCY] fails to boot cloud-image due to host kvm fail

Status in QEMU:
  Confirmed

Bug description:
  On booting the cloud image using qemu/kvm fails with the following
  error:

  Cloud-init v. 0.7.3 running 'init' at Thu, 03 Oct 2013 16:45:21 +0000. Up 
360.78 seconds.
  ci-info: +++++++++++++++++++++++++Net device info+++++++++++++++++++++++++
  ci-info: +--------+------+-----------+---------------+-------------------+
  ci-info: | Device | Up | Address | Mask | Hw-Address |
  ci-info: +--------+------+-----------+---------------+-------------------+
  ci-info: | lo | True | 127.0.0.1 | 255.0.0.0 | . |
  ci-info: | eth0 | True | 10.0.2.15 | 255.255.255.0 | 52:54:00:12:34:56 |
  ci-info: +--------+------+-----------+---------------+-------------------+
  ci-info: ++++++++++++++++++++++++++++++Route 
info++++++++++++++++++++++++++++++
  ci-info: 
+-------+-------------+----------+---------------+-----------+-------+
  ci-info: | Route | Destination | Gateway | Genmask | Interface | Flags |
  ci-info: 
+-------+-------------+----------+---------------+-----------+-------+
  ci-info: | 0 | 0.0.0.0 | 10.0.2.2 | 0.0.0.0 | eth0 | UG |
  ci-info: | 1 | 10.0.2.0 | 0.0.0.0 | 255.255.255.0 | eth0 | U |
  ci-info: 
+-------+-------------+----------+---------------+-----------+-------+
  error: kvm run failed Function not implemented

  /usr/lib/python2.7/dist-
  packages/cloudinit/sources/DataSourceAltCloud.py assumes that
  dmidecode command is availabe (ie it assumes that system is x86) on
  arm systems there is no dmidecode command so host kvm fails with the
  message "error: kvm run failed Function not implemented"

  The patch makes get_cloud_type() function return with UNKNOWN for ARM
  systems.

  I was able to boot the cloud-image on ARM after applying this change.

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