bug#27636: /dev/kvm went missing on i686, Linux 4.12

bug#27636: /dev/kvm went missing on i686, Linux 4.12

[Ricardo Wurmus]

Since the update to Linux 4.12 my i686 machine no longer has /dev/kvm.
I ran “modprobe kvm” successfully, and “lsmod” shows “kvm”, but the
device node does not exist.

Running “modprobe kvm-intel” prints:

    modprobe: ERROR: could not insert 'kvm_intel': Input/output error

-- 
Ricardo

GPG: BCA6 89B6 3655 3801 C3C6  2150 197A 5888 235F ACAC
https://elephly.net

bug#27636: /dev/kvm went missing on i686, Linux 4.12

[Leo Famulari]

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On Mon, Jul 10, 2017 at 07:40:51AM +0200, Ricardo Wurmus wrote:
> Since the update to Linux 4.12 my i686 machine no longer has /dev/kvm.
> I ran “modprobe kvm” successfully, and “lsmod” shows “kvm”, but the
> device node does not exist.
> 
> Running “modprobe kvm-intel” prints:
> 
>     modprobe: ERROR: could not insert 'kvm_intel': Input/output error

I see the same thing on x86_64, but also with older kernels (at least
the 4.11 series).

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bug#27636: /dev/kvm went missing on i686, Linux 4.12

[Mark H Weaver]

Ricardo Wurmus <rekado@elephly.net> writes:

> Since the update to Linux 4.12 my i686 machine no longer has /dev/kvm.
> I ran “modprobe kvm” successfully, and “lsmod” shows “kvm”, but the
> device node does not exist.
>
> Running “modprobe kvm-intel” prints:
>
>     modprobe: ERROR: could not insert 'kvm_intel': Input/output error

Does the kernel message buffer mention anything about "kvm" or "KVM"?

  dmesg | grep -i kvm

      Mark

bug#27636: /dev/kvm went missing on i686, Linux 4.12

[Ricardo Wurmus]

Mark H Weaver <mhw@netris.org> writes:

> Ricardo Wurmus <rekado@elephly.net> writes:
>
>> Since the update to Linux 4.12 my i686 machine no longer has /dev/kvm.
>> I ran “modprobe kvm” successfully, and “lsmod” shows “kvm”, but the
>> device node does not exist.
>>
>> Running “modprobe kvm-intel” prints:
>>
>>     modprobe: ERROR: could not insert 'kvm_intel': Input/output error
>
> Does the kernel message buffer mention anything about "kvm" or "KVM"?
>
>   dmesg | grep -i kvm

No, there is no mention of “kvm” or “KVM” in the kernel messages.

--
Ricardo

GPG: BCA6 89B6 3655 3801 C3C6  2150 197A 5888 235F ACAC
https://elephly.net

bug#27636: /dev/kvm went missing on i686, Linux 4.12

[Mark H Weaver]

Ricardo Wurmus <rekado@elephly.net> writes:

> Mark H Weaver <mhw@netris.org> writes:
>
>> Ricardo Wurmus <rekado@elephly.net> writes:
>>
>>> Since the update to Linux 4.12 my i686 machine no longer has /dev/kvm.
>>> I ran “modprobe kvm” successfully, and “lsmod” shows “kvm”, but the
>>> device node does not exist.
>>>
>>> Running “modprobe kvm-intel” prints:
>>>
>>>     modprobe: ERROR: could not insert 'kvm_intel': Input/output error
>>
>> Does the kernel message buffer mention anything about "kvm" or "KVM"?
>>
>>   dmesg | grep -i kvm
>
> No, there is no mention of “kvm” or “KVM” in the kernel messages.

When you looked for "kvm" or "KVM", did your kernel message buffer still
include the initial boot messages?  The kernel message buffer is of a
fixed size, so eventually the early messages are lost.

The reason I ask is because I did some web searches looking for other
people with the same problem, and what I found was that there was
typically a kernel message at boot time explaining why KVM was disabled.

In my case, on my Thinkpad X200 (which I'm sorry to say is running a
proprietary BIOS for now, because I had to replace the motherboard
recently and haven't yet gotten around to buying the needed clip to
reflash) I see the message "kvm: disabled by bios".

I'm fairly sure that I've seen /dev/kvm on this machine in the past.  It
might be that in earlier versions of Linux, /dev/kvm was created even
when it couldn't be used, and now it's created only conditionally, but
that's only a guess.

I haven't made any changes to the kernel configuration except to add
support for new modules and features as they become available, and as
far as I can see, the relevant KVM options are enabled just as they have
been in the past.

If all else fails, you could try using the 4.9 or 4.4 kernel and see if
that makes any difference.

       Mark

bug#27636: /dev/kvm went missing on i686, Linux 4.12

[Ricardo Wurmus]

Mark H Weaver <mhw@netris.org> writes:

> When you looked for "kvm" or "KVM", did your kernel message buffer still
> include the initial boot messages?  The kernel message buffer is of a
> fixed size, so eventually the early messages are lost.

I ran it immediately after booting 4.12.

> I'm fairly sure that I've seen /dev/kvm on this machine in the past.  It
> might be that in earlier versions of Linux, /dev/kvm was created even
> when it couldn't be used, and now it's created only conditionally, but
> that's only a guess.

I have seen it in the past as well.  It is only with 4.12 that /dev/kvm
is gone.  I have installed 4.9 on this machine and /dev/kvm exists.

-- 
Ricardo

GPG: BCA6 89B6 3655 3801 C3C6  2150 197A 5888 235F ACAC
https://elephly.net

bug#27636: /dev/kvm went missing on i686, Linux 4.12

[Chris Marusich]

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Ricardo Wurmus <rekado@elephly.net> writes:

> Since the update to Linux 4.12 my i686 machine no longer has /dev/kvm.
> I ran “modprobe kvm” successfully, and “lsmod” shows “kvm”, but the
> device node does not exist.
>
> Running “modprobe kvm-intel” prints:
>
>     modprobe: ERROR: could not insert 'kvm_intel': Input/output error

Is this still an issue for you?

-- 
Chris

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bug#27636: /dev/kvm went missing on i686, Linux 4.12

[Leo Famulari]

On Sat, Jun 22, 2019 at 09:13:37PM -0700, Chris Marusich wrote:
> Is this still an issue for you?

Closing due to lack of interest.