Bug 662701

This seems to leave us in a situation where we have to pass this
parameter in order to have any sort of performance, but we'll fail
unnecessarily if KVM is not available, and with no way to really tell
if KVM will work.

I don't think this is the right way to solve this bug, even for
libvirt.

What we really need here are capabilities.

Until we'll get capabilities and guestfish to use libvirt this is an intermediate solution

This bug is about a difference in behavior between RHEL-6 and upstream.  Libvirt is not prepared for this difference; it expects and relies on the upstream behavior.

Whether the upstream behavior is ideal for all use cases is a different question, outside the scope of this bug.  Discussion of this question belongs upstream.

It's pretty much consensus that we could use a structured way to query QEMU "capabilities".  But that's also outside the scope of this bug. "Capabilities" need to be developed upstream.

We had some discussion on IRC and it looks like the way
we are currently doing it will continue to work even with
this change.

Go ahead and we'll check it still works in QA.

I tested 

Upstream        |  default  |-enable-kvm|
----------------+-----------+-----------+
KVM available   | disabled  |  enabled  |
KVM unavailable | disabled  |    fail   |

RHEL-6          |  default  |-enable-kvm|
----------------+-----------+-----------+
KVM available   |  enabled* |  enabled  |
KVM unavailable | disabled  | disabled* |

* deviates from upstream

The deviation in the bottom-right case is the one originally reported.

The deviation in the top-left case is not covered by the original report.

I'd like to realign RHEL-6 with upstream, i.e. remove both deviations. 


Details:

Upstream, KVM available:
$ qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio -enable-kvm
QEMU 0.13.50 monitor - type 'help' for more information
(qemu) info kvm
kvm support: enabled
(qemu) q
$ qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio
QEMU 0.13.50 monitor - type 'help' for more information
(qemu) info kvm
kvm support: disabled
(qemu) q

Upstream, KVM unavailable:
$ qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio -enable-kvm
Could not access KVM kernel module: Permission denied
failed to initialize KVM: Permission denied
[Exit 1 ]
$ qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio
QEMU 0.13.50 monitor - type 'help' for more information
(qemu) info kvm
kvm support: disabled
(qemu) q

RHEL-6, KVM available:
$ qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio -enable-kvm
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: enabled
(qemu) q
$ qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: enabled
(qemu) q

RHEL-6, KVM unavailable:
$ qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio -enable-kvm
open /dev/kvm: Permission denied
Could not initialize KVM, will disable KVM support
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: disabled
(qemu) q
$ qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio
open /dev/kvm: Permission denied
Could not initialize KVM, will disable KVM support
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: disabled
(qemu) q

Comment#6's "upstream" means "upstream QEMU".  There's also qemu-kvm. Turns out that it differs from upstream QEMU exactly the same way as RHEL-6.  What a mess.


Details:

Upstream qemu-kvm, KVM available:
$ ~/work/qemu-kvm/bld-x86/x86_64-softmmu/qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio -enable-kvm
QEMU 0.13.50 monitor - type 'help' for more information
(qemu) info kvm
kvm support: enabled
(qemu) q
$ ~/work/qemu-kvm/bld-x86/x86_64-softmmu/qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio
QEMU 0.13.50 monitor - type 'help' for more information
(qemu) info kvm
kvm support: enabled
(qemu) q

Upstream qemu-kvm, KVM unavailable:
$ ~/work/qemu-kvm/bld-x86/x86_64-softmmu/qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio -enable-kvm
open /dev/kvm: Permission denied
Could not initialize KVM, will disable KVM support
QEMU 0.13.50 monitor - type 'help' for more information
(qemu) info kvm
kvm support: disabled
(qemu) q
$ ~/work/qemu-kvm/bld-x86/x86_64-softmmu/qemu-system-x86_64 -nodefaults -usb -vnc :0 -S -monitor stdio
open /dev/kvm: Permission denied
Could not initialize KVM, will disable KVM support
QEMU 0.13.50 monitor - type 'help' for more information
(qemu) info kvm 
kvm support: disabled
(qemu) q

The problem is that qemu-kvm is expecting KVM to be enabled for default,
and if we start failing if KVM is not available, it means you can only use
qemu-kvm without kvm if you explicitly specify --disable-kvm

There are two ways to handle this:
1) Fail qemu-kvm if KVM is not available, independent on whether --enable-kvm
   is specified.
2) Add an additional internal flag to track whether --enable-kvm was specified
   on the command line, and fail if it was, when KVM is not enabled.

IMHO 2) is really ugly, but I doubt 1) would fly with qemu-kvm maintainers.

Jes

Fixed in upstream qemu-kvm commit b724fa4b.

qemu-kvm        |  default  |-enable-kvm|  -no-kvm
----------------+-----------+-----------+-----------
KVM available   |  enabled* |  enabled  |  disabled
KVM unavailable | disabled  |    fail+  |  disabled

* still differs from upstream qemu
+ changed from disabled

*** Bug 661767 has been marked as a duplicate of this bug. ***

Can reproduce on following package:
$ rpm -qa|grep qemu
qemu-kvm-0.12.1.2-2.147.el6.x86_64

qemu-kvm        |  default  |-enable-kvm|  -no-kvm
----------------+-----------+-----------+-----------
KVM available   |  enabled  |  enabled  |  disabled
KVM unavailable | disabled  |  disabled |  disabled



Verified on package:
$ rpm -qa|grep qemu
qemu-kvm-0.12.1.2-2.148.el6.x86_64

Steps:
1. launch qemu-kvm with kvm available
$ ls -l /dev/kvm
crw-rw-rw-+ 1 root kvm 10, 232 Feb 22 16:23 /dev/kvm
$ /usr/libexec/qemu-kvm -nodefaults -usb -vnc :0 -S -monitor stdio -enable-kvm
Using CPU model "cpu64-rhel6"
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: enabled
(qemu) q

***Actual Result***:
with -enable-kvm, kvm enabled

$ /usr/libexec/qemu-kvm -nodefaults -usb -vnc :0 -S -monitor stdio 
Using CPU model "cpu64-rhel6"
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: enabled
(qemu) q

***Actual Result***
by default, kvm enabled

$ /usr/libexec/qemu-kvm -nodefaults -usb -vnc :0 -S -monitor stdio -no-kvm
Using CPU model "cpu64-rhel6"
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: disabled
(qemu) q

***Actual Result***
with -no-kvm, kvm disabled

2. launch qemu-kvm with kvm unavailable.
$ ls -l /dev/kvm
crw-------+ 1 root kvm 10, 232 Feb 22 16:23 /dev/kvm
$ /usr/libexec/qemu-kvm -nodefaults -usb -vnc :0 -S -monitor stdio -enable-kvm
open /dev/kvm: Permission denied
failed to initialize KVM: Operation not permitted

***Actual Result***
with -enable-kvm, failed

$ /usr/libexec/qemu-kvm -nodefaults -usb -vnc :0 -S -monitor stdio 
open /dev/kvm: Permission denied
Could not initialize KVM, will disable KVM support
Using CPU model "cpu64-rhel6"
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: disabled
(qemu) q

***Actual Result***
by default, kvm disabled

$ /usr/libexec/qemu-kvm -nodefaults -usb -vnc :0 -S -monitor stdio -no-kvm
Using CPU model "cpu64-rhel6"
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: disabled
(qemu) q

***Actual Result***
with -no-kvm, kvm disabled

Renamed /dev/kvm, and verify again.
# /usr/libexec/qemu-kvm -nodefaults -usb -vnc :0 -S -monitor stdio -enable-kvm
open /dev/kvm: No such file or directory
failed to initialize KVM: Operation not permitted

***Actual Result***:
with -enable-kvm, failed.

# /usr/libexec/qemu-kvm -nodefaults -usb -vnc :0 -S -monitor stdio 
open /dev/kvm: No such file or directory
Could not initialize KVM, will disable KVM support
Using CPU model "cpu64-rhel6"
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: disabled
(qemu) q

***Actual Result***:
by default, kvm disabled

# /usr/libexec/qemu-kvm -nodefaults -usb -vnc :0 -S -monitor stdio -no-kvm
Using CPU model "cpu64-rhel6"
QEMU 0.12.1 monitor - type 'help' for more information
(qemu) info kvm
kvm support: disabled
(qemu) q

***Actual Result***:
with -no-kvm, kvm disabled

So, I think this issue got fixed.

move to verified based on comment#16 and comment#19

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2011-0534.html

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2011-0534.html