[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Brad Figg]

** Tags added: cscc

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Title:
  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Frank Heimes]

Since we already reached the stabilization phase of xenial/16.04 with .5 (and 
.6), with the focus on stability and security, and because this is not a really 
bug, rather than 'nice to have' to _not_ show /dev/kvm in case already running 
virtualized on KVM (because nested KVM is not supported on s390x), I'm now 
going to change this Bug to Won't Fix.
In anybody objects please leave a comment ...

** Changed in: ubuntu-z-systems
   Status: Triaged => Won't Fix

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  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Frank Heimes]

Lowering importance to Low due to currently different focus.

** Changed in: ubuntu-z-systems
   Importance: Medium => Low

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Title:
  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Frank Heimes]

Sorry for the delay - got a bit distracted by other topics.

Just did a retest with
"linux-image-4.4.0-116-generic_4.4.0-116.140~lp1735420ModifiedAnnotations_s390x.deb"
but still can see the kvm device:

ubuntu@ubu-vm-01:~$ uname -a
Linux ubu-vm-01 4.4.0-116-generic #140~lp1735420ModifiedAnnotations SMP Wed Mar 
21 17:57:02 UTC 20 s390x s390x s390x GNU/Linux
ubuntu@ubu-vm-01:~$ kvm-ok 
INFO: /dev/kvm exists
KVM acceleration can be used
ubuntu@ubu-vm-01:~$ ls -la /dev/kvm
crw-rw 1 root kvm 10, 232 Mar 27 01:45 /dev/kvm
ubuntu@ubu-vm-01:~$

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Title:
  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Joseph Salisbury]

I noted a difference between the two configs.  The v4.10-rc3 config has
the KVM module built in.  However, the v4.10-rc2 config has KVM built in
for the config file, but was still set to module in the annotations
file.

I fixed the annotations file and built a Xenial test kernel.

The test kernel can be downloaded from:
http://kernel.ubuntu.com/~jsalisbury/lp1735420/

Can you test this kernel and see if it resolves the bug?

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  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Joseph Salisbury]

Hmm, it could also be a config change that is needed.  The 4.10-rc2
kernel uses the 4.9.0-2.3 configs and the 4.10-rc3 kernel uses the
4.10.0-0.2 config.  I'll compare those two as well.

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  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Joseph Salisbury]

Yeah,  I couldn't find anything specific in v4.10-rc3 either.  I'll
start a reverse bisect to see which commit that points to.  It will take
testing of about 7 or so test kernels.

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Title:
  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Frank Heimes]

Well, does not seem to be in:

ubuntu@ubu-vm-01:~$ uname -a
Linux ubu-vm-01 4.4.0-116-generic #140~lp1735420Commitcabab3f SMP Tue Mar 20 
20:07:24 UTC 2018 s390x s390x s390x GNU/Linux
ubuntu@ubu-vm-01:~$ kvm-ok 
INFO: /dev/kvm exists
KVM acceleration can be used
ubuntu@ubu-vm-01:~$ ls -la /dev/kvm 
crw-rw 1 root kvm 10, 232 Mar 20 12:17 /dev/kvm

Interestingly I couldn't find any indication in the 4.10.0-041000rc3
changes file that point to this functionality ...

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Title:
  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Joseph Salisbury]

There was only one commit that sticks out between 4.10-rc2 and
v4.10-rc3, it is kvm and s390 related:

cabab3f ("s390/kbuild: enable modversions for symbols exported from
asm")

I built a Xenial test kernel with a pick of this commit.  The test kernel can 
be downloaded from:
http://kernel.ubuntu.com/~jsalisbury/lp1735420/

Can you test this kernel and see if it resolves the bug?  If it does
not, we'll have to reverse bisect to identify the commit.

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Title:
  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Frank Heimes]

I tried some more:

4.10 rc3 does have the patch:
ubuntu@ubu-vm-01:~$ uname -a
Linux ubu-vm-01 4.10.0-041000rc3-generic #201701081831 SMP Mon Jan 9 00:34:16 
UTC 2017 s390x s390x s390x GNU/Linux
ubuntu@ubu-vm-01:~$ kvm-ok 
INFO: /dev/kvm does not exist
HINT:   sudo modprobe kvm
INFO: For more detailed results, you should run this as root
HINT:   sudo /usr/sbin/kvm-ok
ubuntu@ubu-vm-01:~$ ls -la /dev/kvm
ls: cannot access '/dev/kvm': No such file or directory

4.10-rc2 seems to be the last one without:

ubuntu@ubu-vm-01:~$ uname -a
Linux ubu-vm-01 4.10.0-041000rc2-generic #201701011831 SMP Mon Jan 2 00:41:33 
UTC 2017 s390x s390x s390x GNU/Linux
ubuntu@ubu-vm-01:~$ kvm-ok 
INFO: /dev/kvm exists
KVM acceleration can be used
ubuntu@ubu-vm-01:~$ ls -la /dev/kvm
crw--- 1 root root 10, 232 Mar 20 07:41 /dev/kvm

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Frank Heimes]

Doesn't seem to be in - kvm device still there:

ubuntu@ubu-vm-01:~$ uname -a
Linux ubu-vm-01 4.10.0-041000rc1-generic #201612252031 SMP Mon Dec 26 02:37:39 
UTC 2016 s390x s390x s390x GNU/Linux
ubuntu@ubu-vm-01:~$ kvm-ok 
INFO: /dev/kvm exists
KVM acceleration can be used
ubuntu@ubu-vm-01:~$ ls -la /dev/kvm
crw--- 1 root root 10, 232 Mar 20 07:34 /dev/kvm

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  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Joseph Salisbury]

Can you see if the patch is in v4.10-rc1:
http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.10-rc1/

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Title:
  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Frank Heimes]

Mainline Kernel 4.8 does not seem to have the patch included:

ubuntu@ubu-vm-01:~$ uname -a
Linux ubu-vm-01 4.8.0-040800-generic #201610022031 SMP Mon Oct 3 02:27:31 UTC 
2016 s390x s390x s390x GNU/Linux
ubuntu@ubu-vm-01:~$ kvm-ok 
INFO: /dev/kvm exists
KVM acceleration can be used
ubuntu@ubu-vm-01:~$ ls -la /dev/kvm
crw--- 1 root root 10, 232 Mar 20 05:16 /dev/kvm

Knowing that it is in 4.13, I tried mainline 4.10 as well and - yes - it
must have the patch:

ubuntu@ubu-vm-01:~$ uname -a
Linux ubu-vm-01 4.10.0-041000-generic #201702191831 SMP Mon Feb 20 00:15:43 UTC 
2017 s390x s390x s390x GNU/Linux
ubuntu@ubu-vm-01:~$ kvm-ok 
INFO: /dev/kvm does not exist
HINT:   sudo modprobe kvm
INFO: For more detailed results, you should run this as root
HINT:   sudo /usr/sbin/kvm-ok
ubuntu@ubu-vm-01:~$ ls -la /dev/kvm
ls: cannot access '/dev/kvm': No such file or directory
ubuntu@ubu-vm-01:~$

So looks like the patch came in with either 4.9 or 4.10 (probably 4.10).

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Title:
  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Joseph Salisbury]

Since we don't know the commit that would solve this off hand, we can
perform a "Reverse" bisect to identify that commit.

Can you see if the following kernel has the bug:
http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.8/

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  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Frank Heimes]

So I just did a brief test - stock kernel first and then the modified
one:

ubuntu@ubu-vm-01:~$ uname -a
Linux ubu-vm-01 4.4.0-116-generic #140-Ubuntu SMP Mon Feb 12 21:21:31 UTC 2018 
s390x s390x s390x GNU/Linux
ubuntu@ubu-vm-01:~$ ls -la /dev/kvm 
crw--- 1 root root 10, 232 Mar 13 22:42 /dev/kvm

ubuntu@ubu-vm-01:~$ uname -a
Linux ubu-vm-01 4.4.0-116-generic #140~lp1735420 SMP Tue Mar 13 21:48:51 UTC 
2018 s390x s390x s390x GNU/Linux
ubuntu@ubu-vm-01:~$ ls -la /dev/kvm 
crw--- 1 root root 10, 232 Mar 14 03:47 /dev/kvm
ubuntu@ubu-vm-01:~$ kvm-ok 
INFO: /dev/kvm exists
KVM acceleration can be used
ubuntu@ubu-vm-01:~$

So I couldn't identify a difference between both kernels so far ...

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Re: [Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Frank Heimes]

Hi Joe,
yes that should be easy for me to test.
I think I only need to run that patched xenial kernel in a KVM virtual
machine and the device shouldn't be there - however running it directly in
LPAR should show the device.

I'm off on Wednesday, but will test it later this week.

Bye, Frank


Frank Heimes | Tech. Lead Ubuntu Server on Z | Canonical Ltd.
mail: frank.hei...@canonical.com
irc: jfh
www.canonical.com | www.ubuntu.com | ubuntu-on-big-iron.blogspot.com


On Tue, Mar 13, 2018 at 10:55 PM, Joseph Salisbury <
joseph.salisb...@canonical.com> wrote:

> Frank, Is there a way to test a test kernel I built?  I built a Xenial
> test kernel with a back port of commit a411edf1320e ("KVM: s390: vsie:
> add module parameter "nested"").
>
> I'm not sure off hand if just this commit is needed or if there are
> others as well.
>
> The test kernel can be downloaded from:
> http://kernel.ubuntu.com/~jsalisbury/lp1735420/
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1735420
>
> Title:
>   Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x
>
> Status in Ubuntu on IBM z Systems:
>   Triaged
> Status in linux package in Ubuntu:
>   Triaged
> Status in linux source package in Xenial:
>   Triaged
>
> Bug description:
>   Since nested virtualization with KVM is not supported on s390x, please
> disable this in Xenial - in case it's doable with reasonable effort.
>   (I think it was already disabled for later Ubuntu releases ... was also
> discussed on IRC)
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ubuntu-z-systems/+bug/1735420/+subscriptions
>

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  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Joseph Salisbury]

Frank, Is there a way to test a test kernel I built?  I built a Xenial
test kernel with a back port of commit a411edf1320e ("KVM: s390: vsie:
add module parameter "nested"").

I'm not sure off hand if just this commit is needed or if there are
others as well.

The test kernel can be downloaded from:
http://kernel.ubuntu.com/~jsalisbury/lp1735420/

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  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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[Bug 1735420] Re: Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

[Joseph Salisbury]

** Also affects: linux (Ubuntu)
   Importance: Undecided
   Status: New

** Changed in: linux (Ubuntu)
   Status: New => Triaged

** Changed in: linux (Ubuntu)
   Importance: Undecided => Medium

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
   Status: New

** Changed in: linux (Ubuntu Xenial)
   Importance: Undecided => Medium

** Changed in: linux (Ubuntu Xenial)
   Status: New => Triaged

** Changed in: linux (Ubuntu)
 Assignee: (unassigned) => Canonical Kernel Team (canonical-kernel-team)

** Changed in: linux (Ubuntu Xenial)
 Assignee: (unassigned) => Canonical Kernel Team (canonical-kernel-team)

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  Avoid creation of /dev/kvm in Xenial KVM virtual machines on s390x

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