Bug 130113 - Strange output of /proc/mtrr
Strange output of /proc/mtrr
Product: Red Hat Enterprise Linux 3
Classification: Red Hat
Component: kernel (Show other bugs)
x86_64 Linux
medium Severity low
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Assigned To: Larry Woodman
Brian Brock
Depends On:
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Reported: 2004-08-17 05:10 EDT by Rainer Koenig
Modified: 2007-11-30 17:07 EST (History)
3 users (show)

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2005-02-16 17:37:34 EST
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RHEL 7.3 requirements from Atomic Host:
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Description Rainer Koenig 2004-08-17 05:10:00 EDT
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Description of problem:
A `cat /proc/mtrr` displays "strange" looking values for the size on
Intel based x86_64 (EM64T plattform) systems. It looks like that the
displayed size is 16 times bigger than the real size of that memory

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

How reproducible:

Steps to Reproduce:
1. Install Red Hat EL 3 Upd. 3 beta on Intel based x86_64 system
2. Login as root 
3. cat /proc/mtrr

Actual Results:  Here an example of the x86_64 version of RHEL 3: 

[root@localhost root]# uname -a
Linux localhost.localdomain 2.4.21-17.EL #1 SMP Thu Jul 8 19:34:05 EDT
2004 x86_64 x86_64 x86_64 GNU/Linux
[root@localhost root]# cat /proc/mtrr
reg00: base=0x00000000 (   0MB), size=8192MB: write-back, count=1
reg01: base=0x1ff00000 ( 511MB), size=  16MB: uncachable, count=1
[root@localhost root]#

Note that the machine is only eqipped with 512 MB of RAM.

Expected Results:  Same as above, but this time the 32-bit Version of
RHEL 3 Upd. 2:

[root@localhost root]# uname -a
Linux localhost.localdomain 2.4.21-15.ELsmp #1 SMP Thu Apr 22 00:18:24
EDT 2004 i686 i686 i386 GNU/Linux
[root@localhost root]# cat /proc/mtrr
reg00: base=0x00000000 (   0MB), size= 512MB: write-back, count=1
reg01: base=0x1ff00000 ( 511MB), size=   1MB: uncachable, count=1
reg02: base=0xf0000000 (3840MB), size=  16MB: write-combining, count=1
[root@localhost root]#

Identical hardware, here 512 MB size is displayed as expected. 

Additional info:

Looks like this bug is only occuring on Intel based systems. I've seen
it on a Prescott (examples above) but also on a Dual Xeon workstation.
A dual opteron workstation seems not to be affected by this.

On the same hardware the 2.6.5 kernel of SuSE distribution shows no
error in the size. 

I just want to report this as a minor bug, impacts on other things
(like 3D graphics) are not observed so far. But we just made a few
minor tests.
Comment 1 Jim Paradis 2005-02-16 17:24:41 EST
Reassigning to lwoodman as he looked at it and came up with the fix.
Comment 2 Jim Paradis 2005-02-16 17:37:34 EST

*** This bug has been marked as a duplicate of 137201 ***
Comment 3 Ernie Petrides 2005-02-19 05:07:09 EST
A fix for this problem has just been committed to the RHEL3 U5
patch pool this evening (in kernel version 2.4.21-27.16.EL).
Comment 4 Tim Powers 2005-05-18 09:27:47 EDT
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.


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