Bug 193241 - Microcode device /dev/cpu/microcode doesn't exist?
Microcode device /dev/cpu/microcode doesn't exist?
Product: Fedora
Classification: Fedora
Component: kernel (Show other bugs)
i686 Linux
medium Severity medium
: ---
: ---
Assigned To: Jon Masters
Depends On:
  Show dependency treegraph
Reported: 2006-05-26 10:55 EDT by Robert Scheck
Modified: 2007-11-30 17:11 EST (History)
1 user (show)

See Also:
Fixed In Version: 2.6.23-0.157.rc4.git2
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2007-09-05 18:10:29 EDT
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)

  None (edit)
Description Robert Scheck 2006-05-26 10:55:47 EDT
Description of problem:
> service microcode_ctl start
Applying Intel CPU microcode update: /etc/init.d/microcode_ctl: microcode
device /dev/cpu/microcode doesn't exist?

And yepp, the script is correct:

> ls -l /dev/cpu*
ls: /dev/cpu*: No such file or directory

WHY is this the case?! CPU is:
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 2
model name      : Intel(R) Xeon(TM) CPU 3.06GHz
stepping        : 9
cpu MHz         : 3066.228
cache size      : 512 KB

Version-Release number of selected component (if applicable):

How reproducible:
Everytime, see above.

Actual results:
Microcode device /dev/cpu/microcode doesn't exist.

Expected results:
Existing microcode device /dev/cpu/microcode or similar ;-)

Additional info:
Maybe this bug is assigned to the wrong component, reassign to kernel, udev
or whatever fits if needed - thank you.
Comment 1 Jon Masters 2006-09-01 00:55:57 EDT
I need to know the version of the kernel that you are running this against so
that I can try to track down why that device does not exist. Please let me know.
Comment 2 Robert Scheck 2006-09-01 07:31:04 EDT
2.6.17-1.2293_FC6 - which is pretty old now. But it was up2date when I wrote 
this bug report...
Comment 3 Hong-Gunn Chew 2007-04-05 01:55:23 EDT
It seems that the microcode module is not created in fc6.  Something might have
changed since fc5 to make the decision to remove the module?


Comment 4 Robert Scheck 2007-07-15 15:43:21 EDT
Comment 5 Jon Masters 2007-08-20 02:38:42 EDT
This is a potential bug in the kernel config. Both in xen and non-xen kernels
(in the case of Xen, the hypervisor needs a fix to do microcode updates...and
even then, it's implemented incorrectly wrt. how it should be done in Xen, but
that requires a complete re-architecting of Xen itself to fix).

Comment 6 Robert Scheck 2007-08-20 16:57:40 EDT
Well...it isn't of belong to me. Novell has microcode_ctl working with and 
without Xen, so why aren't we able? I'm not sure, what you would like to hear 
from me but: This is no notabug, no cantfix, no wontfix...but: Assigned :)
Comment 7 Jon Masters 2007-08-20 18:11:00 EDT
Yes, but it's not a bug in the microcode package. It's a "bug" in the

Note that I'm not saying it doesn't work, I'm saying that the Xen implementation
of microcode updates is known to be insufficient in the longer term - it works,
but I've been told that, once the CPU is in VT mode, that you should not be
trying to update the microcode after that...it should be done in the hypervisor
well before booting the first DomU or even Dom0. It's not a Novell-vs-RedHat
thing. It's just that Xen will need some tweaking in future to handle this IMO.

Comment 8 Robert Scheck 2007-09-05 18:10:29 EDT
$ grep CONFIG_MICROCODE /boot/config-2.6.23-0.157.rc4.git2

Note You need to log in before you can comment on or make changes to this bug.