KVM on old kernels pre-2.6.28

KVM on old kernels pre-2.6.28

[Asdo]

Some time ago in this list it was mentioned that old kernels pre-2.6.28
don't work well with KVM.
(in particular we have a machine with 2.6.24)

Unfortunately the type of problem was not mentioned in the posts I could
find. Is that a performance problem, a stability problem, or a data
corruption problem... ?

And I would also like to know if the "problem" can be worked around by
installing a new kvm-kmod like 2.6.36.2  or we really need to upgrade
the whole kernel to get rid of it.

(I was thinking at installing a new qemu-kvm like the 0.12.5 on that)

Thank you in advance

Re: KVM on old kernels pre-2.6.28

[Avi Kivity]

On 01/26/2011 06:51 PM, Asdo wrote:
> Some time ago in this list it was mentioned that old kernels pre-2.6.28
> don't work well with KVM.
> (in particular we have a machine with 2.6.24)
>

pre 2.6.27 kernels don't have mmu notifiers and thus don't handle 
overcommit well.  No idea if there's anything wrong with 2.6.27 itself.

> Unfortunately the type of problem was not mentioned in the posts I could
> find. Is that a performance problem, a stability problem, or a data
> corruption problem... ?
>
> And I would also like to know if the "problem" can be worked around by
> installing a new kvm-kmod like 2.6.36.2  or we really need to upgrade
> the whole kernel to get rid of it.

The mmu notifier issue requires 2.6.27 or above.  Using kvm-kmod allows 
you to run a newer kvm on an older kernel, but doesn't fix 
infrastructure issues like I mentioned.

> (I was thinking at installing a new qemu-kvm like the 0.12.5 on that)

0.12.5 is already old.  But why are you running such old and unsupported 
kernels?  I recommend either running a distribution kernel, where 
someone takes care of bug fixes and security updates, or running one of 
the stable tree kernels.

-- 
error compiling committee.c: too many arguments to function

Re: KVM on old kernels pre-2.6.28

[David Ahern]

On 01/27/11 02:55, Avi Kivity wrote:
> On 01/26/2011 06:51 PM, Asdo wrote:
>> Some time ago in this list it was mentioned that old kernels pre-2.6.28
>> don't work well with KVM.
>> (in particular we have a machine with 2.6.24)
>>
> 
> pre 2.6.27 kernels don't have mmu notifiers and thus don't handle
> overcommit well.  No idea if there's anything wrong with 2.6.27 itself.

The KVM code in the 2.6.27 kernel is broken. qemu-kvm emits:

KVM kernel module broken (DESTROY_MEMORY_REGION).
Please upgrade to at least kernel 2.6.29 or recent kvm-kmod
(see http://sourceforge.net/projects/kvm).

You'll need to use newer kvm-kmod versions.

David

Re: KVM on old kernels pre-2.6.28

[Avi Kivity]

On 01/27/2011 08:09 PM, David Ahern wrote:
>
> On 01/27/11 02:55, Avi Kivity wrote:
> >  On 01/26/2011 06:51 PM, Asdo wrote:
> >>  Some time ago in this list it was mentioned that old kernels pre-2.6.28
> >>  don't work well with KVM.
> >>  (in particular we have a machine with 2.6.24)
> >>
> >
> >  pre 2.6.27 kernels don't have mmu notifiers and thus don't handle
> >  overcommit well.  No idea if there's anything wrong with 2.6.27 itself.
>
> The KVM code in the 2.6.27 kernel is broken. qemu-kvm emits:
>
> KVM kernel module broken (DESTROY_MEMORY_REGION).
> Please upgrade to at least kernel 2.6.29 or recent kvm-kmod
> (see http://sourceforge.net/projects/kvm).
>
> You'll need to use newer kvm-kmod versions.

Ah, but that's not a host kernel issue.  So you could have 
kvm-kmod-2.6.37 atop 2.6.27 (still I wouldn't recommend it).

-- 
error compiling committee.c: too many arguments to function

Re: KVM on old kernels pre-2.6.28

[David Ahern]

On 01/30/11 06:03, Avi Kivity wrote:

>> The KVM code in the 2.6.27 kernel is broken. qemu-kvm emits:
>>
>> KVM kernel module broken (DESTROY_MEMORY_REGION).
>> Please upgrade to at least kernel 2.6.29 or recent kvm-kmod
>> (see http://sourceforge.net/projects/kvm).
>>
>> You'll need to use newer kvm-kmod versions.
> 
> Ah, but that's not a host kernel issue.  So you could have
> kvm-kmod-2.6.37 atop 2.6.27 (still I wouldn't recommend it).
> 

I don't understand. If the host kernel is 2.6.27, qemu-kvm complains and
refuses to open /dev/kvm. Your options are to upgrade the host kernel or
use a newer kvm-kmod version.

Are you saying kvm-kmod-2.6.37 is not advisable on 2.6.27? What about
kvm-kmod-2.6.32.27?

David

Re: KVM on old kernels pre-2.6.28

[Avi Kivity]

On 01/30/2011 06:37 PM, David Ahern wrote:
>
> On 01/30/11 06:03, Avi Kivity wrote:
>
> >>  The KVM code in the 2.6.27 kernel is broken. qemu-kvm emits:
> >>
> >>  KVM kernel module broken (DESTROY_MEMORY_REGION).
> >>  Please upgrade to at least kernel 2.6.29 or recent kvm-kmod
> >>  (see http://sourceforge.net/projects/kvm).
> >>
> >>  You'll need to use newer kvm-kmod versions.
> >
> >  Ah, but that's not a host kernel issue.  So you could have
> >  kvm-kmod-2.6.37 atop 2.6.27 (still I wouldn't recommend it).
> >
>
> I don't understand. If the host kernel is 2.6.27, qemu-kvm complains and
> refuses to open /dev/kvm. Your options are to upgrade the host kernel or
> use a newer kvm-kmod version.
>
> Are you saying kvm-kmod-2.6.37 is not advisable on 2.6.27? What about
> kvm-kmod-2.6.32.27?

No, that kvm-kmod-2.6.27, or a pure 2.6.27 isn't good.  kvm-kmod-2.6.29+ 
over 2.6.27+ (for mmu notifiers) or a pure 2.6.29+ setup is fine.  If 
you're careful with overcommit you might get away with a pre 2.6.27 host.

(but take all that with a grain of salt, I haven't run kvm-kmod for a 
long while apart from the RHEL 5 version, and I won't recommend anything 
outside a supported distro kernel or an active Linux stable/longterm tree).

-- 
error compiling committee.c: too many arguments to function

Re: KVM on old kernels pre-2.6.28

[Asdo]

On 01/27/2011 10:55 AM, Avi Kivity wrote:
> ... Using kvm-kmod allows you to run a newer kvm on an older kernel ...

ok thanks

Regarding this: I can't find the kmod version requirements for every KVM
version.

What happens if the kernel module version I'm running is too old for the
KVM I'm trying to run? Will it fail at startup giving an error, or I
won't be warned and then weird things will happen sometime during runtime?
If it's the latter, can I at least be sure that always installing the
latest kvm-kmod will not do harm to any KVM, even if the KVM is older?

Thank you

Re: KVM on old kernels pre-2.6.28

[Avi Kivity]

On 02/03/2011 04:33 PM, Asdo wrote:
> On 01/27/2011 10:55 AM, Avi Kivity wrote:
> >  ... Using kvm-kmod allows you to run a newer kvm on an older kernel ...
>
> ok thanks
>
> Regarding this: I can't find the kmod version requirements for every KVM
> version.

I don't think there is an exhaustive list.

> What happens if the kernel module version I'm running is too old for the
> KVM I'm trying to run? Will it fail at startup giving an error, or I
> won't be warned and then weird things will happen sometime during runtime?
> If it's the latter, can I at least be sure that always installing the
> latest kvm-kmod will not do harm to any KVM, even if the KVM is older?

There is no warranty.

-- 
error compiling committee.c: too many arguments to function