upgrade kvm with running vm

upgrade kvm with running vm

[sofa5000]

hi everybody,

is it a problem to update kvm (the kvm package (qemu-kvm on debian) with
the package manager) while some vms are turned on? or should i shutdown
all vms first?

thanks

Re: upgrade kvm with running vm

[Teck Choon Giam]

On Thu, Oct 7, 2010 at 11:43 PM,  <sofa5000@lavabit.com> wrote:
> hi everybody,
>
> is it a problem to update kvm (the kvm package (qemu-kvm on debian) with
> the package manager) while some vms are turned on? or should i shutdown
> all vms first?

>From personal experience (install from source), there shouldn't be a
problem to perform upgrade/update of qemu-kvm without shutting down
those running VMs.  However, in order to use the updated version of
the qemu-kvm, you will need to unload those loaded kvm-intel or
kvm-amd and kvm kernel modules.  Such unloading of modules will need
to shutdown all running VMs in order to successfully unload (rmmod)
those kernel modules.  After unloading, you can reload the updated
version by using modprobe or insmod after you have done depmod.

Hope this helps!

Kindest regards,
Giam Teck Choon

Re: upgrade kvm with running vm

[Michael Tokarev]

08.10.2010 08:07, Teck Choon Giam wrote:
> On Thu, Oct 7, 2010 at 11:43 PM,  <sofa5000@lavabit.com> wrote:
>> hi everybody,
>>
>> is it a problem to update kvm (the kvm package (qemu-kvm on debian) with
>> the package manager) while some vms are turned on? or should i shutdown
>> all vms first?

If you update kvm userspace while some VMs are running, these
VMs will not "pick" the new userspace, they will continue
running by old userspace, until you restart them.  It's just
the same as if you upgrade, say, your shell while it's running -
new sessions will use new shell, alrady running will continue
running using old shell.

> From personal experience (install from source), there shouldn't be a
> problem to perform upgrade/update of qemu-kvm without shutting down
> those running VMs.  However, in order to use the updated version of
> the qemu-kvm, you will need to unload those loaded kvm-intel or
> kvm-amd and kvm kernel modules.  Such unloading of modules will need
> to shutdown all running VMs in order to successfully unload (rmmod)
> those kernel modules.  After unloading, you can reload the updated
> version by using modprobe or insmod after you have done depmod.

Do Not Mess With Kernel Modules (tm).  There's no need to.

/mjt

Re: upgrade kvm with running vm

[Teck Choon Giam]

On Fri, Oct 8, 2010 at 2:03 PM, Michael Tokarev <mjt@tls.msk.ru> wrote:
> 08.10.2010 08:07, Teck Choon Giam wrote:
>> On Thu, Oct 7, 2010 at 11:43 PM,  <sofa5000@lavabit.com> wrote:
>>> hi everybody,
>>>
>>> is it a problem to update kvm (the kvm package (qemu-kvm on debian) with
>>> the package manager) while some vms are turned on? or should i shutdown
>>> all vms first?
>
> If you update kvm userspace while some VMs are running, these
> VMs will not "pick" the new userspace, they will continue
> running by old userspace, until you restart them.  It's just
> the same as if you upgrade, say, your shell while it's running -
> new sessions will use new shell, alrady running will continue
> running using old shell.

I am not sure about userspace wise.  In order to use different version
of qemu-kvm, besides reboot... there is only one method to run
different version such as upgraded version or downgraded version... is
to shutdown all VMs and reload the kvm related kernel modules.

>
>> From personal experience (install from source), there shouldn't be a
>> problem to perform upgrade/update of qemu-kvm without shutting down
>> those running VMs.  However, in order to use the updated version of
>> the qemu-kvm, you will need to unload those loaded kvm-intel or
>> kvm-amd and kvm kernel modules.  Such unloading of modules will need
>> to shutdown all running VMs in order to successfully unload (rmmod)
>> those kernel modules.  After unloading, you can reload the updated
>> version by using modprobe or insmod after you have done depmod.
>
> Do Not Mess With Kernel Modules (tm).  There's no need to.

There is a need to :p

I learnt this due to test different version of qemu-kvm about
system_shutdown stop working for FreeBSD guest VM after 0.12.1 if I
remember correctly.  If I never done this, each test version I will
need to reboot once... so waste of time etc... ...

But I agreed in general about your "Do Not Mess With Kernel Modules
(tm)." ... ...

Thanks.

Kindest regards,
Giam Teck Choon

Re: upgrade kvm with running vm

[Michael Tokarev]

09.10.2010 03:36, Teck Choon Giam wrote:
> On Fri, Oct 8, 2010 at 2:03 PM, Michael Tokarev <mjt@tls.msk.ru> wrote:
[]
> I am not sure about userspace wise.  In order to use different version
> of qemu-kvm, besides reboot... there is only one method to run
> different version such as upgraded version or downgraded version... is
> to shutdown all VMs and reload the kvm related kernel modules.

Someone of us two does not understand something.

Why are you reloading kernel module?  It comes with the kernel,
and if you reloading it, you're rebooting the host, no?  If yes,
why?

[]
>> Do Not Mess With Kernel Modules (tm).  There's no need to.

It was for a reason I mentioned this.  Again: kvm, for quite
some time already, does not come with kernel modules, the
kernel modules comes with your kernel.  You need 2.6.28+
kernel modules to work with any reasonable kvm userspace,
including even kvm-72 from debian lenny.  Earlier kernels
are hopeless for kvm, there were too many various problems
exposed by kvm (this includes debian 2.6.26 kernel).

There's no need to mess with kvm kernel modules.  Unless
you want to use some feature that is present only in some
future release (such as vhost-net for example).  But for
these, it may be better to really upgrate the kernel to
2.6.35+.

/mjt

Re: upgrade kvm with running vm

[Teck Choon Giam]

On Sat, Oct 9, 2010 at 2:37 PM, Michael Tokarev <mjt@tls.msk.ru> wrote:
> 09.10.2010 03:36, Teck Choon Giam wrote:
>> On Fri, Oct 8, 2010 at 2:03 PM, Michael Tokarev <mjt@tls.msk.ru> wrote:
> []
>> I am not sure about userspace wise.  In order to use different version
>> of qemu-kvm, besides reboot... there is only one method to run
>> different version such as upgraded version or downgraded version... is
>> to shutdown all VMs and reload the kvm related kernel modules.
>
> Someone of us two does not understand something.
>
> Why are you reloading kernel module?  It comes with the kernel,
> and if you reloading it, you're rebooting the host, no?  If yes,
> why?

I am not rebooting the server or host.  From my previous reply I
believe I make myself clear that in order to use upgraded or
downgraded
qemu-kvm version, without rebooting the server (host) the only method
is to shutdown all VMs and reload the kvm related modules.  If just
restart all VMs will not run the upgraded/downgraded version of
qemu-kvm without reboot the server (host) or reload kvm related
modules.  This is from my person test experience with vanilla kernel
2.6.32.x.

>
> []
>>> Do Not Mess With Kernel Modules (tm).  There's no need to.
>
> It was for a reason I mentioned this.  Again: kvm, for quite
> some time already, does not come with kernel modules, the
> kernel modules comes with your kernel.  You need 2.6.28+
> kernel modules to work with any reasonable kvm userspace,
> including even kvm-72 from debian lenny.  Earlier kernels
> are hopeless for kvm, there were too many various problems
> exposed by kvm (this includes debian 2.6.26 kernel).
>
> There's no need to mess with kvm kernel modules.  Unless
> you want to use some feature that is present only in some
> future release (such as vhost-net for example).  But for
> these, it may be better to really upgrate the kernel to
> 2.6.35+.

See my above reply about why there is a need to.

Thanks.

Kindest regards,
Giam Teck Choon

Re: upgrade kvm with running vm

[Teck Choon Giam]

On Sat, Oct 9, 2010 at 10:52 PM, Teck Choon Giam
<giamteckchoon@gmail.com> wrote:
> On Sat, Oct 9, 2010 at 2:37 PM, Michael Tokarev <mjt@tls.msk.ru> wrote:
>> 09.10.2010 03:36, Teck Choon Giam wrote:
>>> On Fri, Oct 8, 2010 at 2:03 PM, Michael Tokarev <mjt@tls.msk.ru> wrote:
>> []
>>> I am not sure about userspace wise.  In order to use different version
>>> of qemu-kvm, besides reboot... there is only one method to run
>>> different version such as upgraded version or downgraded version... is
>>> to shutdown all VMs and reload the kvm related kernel modules.
>>
>> Someone of us two does not understand something.
>>
>> Why are you reloading kernel module?  It comes with the kernel,
>> and if you reloading it, you're rebooting the host, no?  If yes,
>> why?
>
> I am not rebooting the server or host.  From my previous reply I
> believe I make myself clear that in order to use upgraded or
> downgraded
> qemu-kvm version, without rebooting the server (host) the only method
> is to shutdown all VMs and reload the kvm related modules.  If just
> restart all VMs will not run the upgraded/downgraded version of
> qemu-kvm without reboot the server (host) or reload kvm related
> modules.  This is from my person test experience with vanilla kernel
> 2.6.32.x.

I just tested and what you said is true for qemu-kvm version
upgrades/downgrades... there is no need to play with the kernel
modules.  Simply restart all VMs works!  Weird about my test
experience few weeks or months back though... ... :/

Thanks.

Kindest regards,
Giam Teck Choon