linux-kernel - Re: [BUG] /proc/mtrr I/O error

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Date:	Tue, 2 Sep 2008 22:58:22 -0500
From:	Bob Tracy <rct@...rkin.frus.com>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] /proc/mtrr I/O error

On Tue, Sep 02, 2008 at 04:08:00PM -0700, Yinghai Lu wrote:
> On Tue, Sep 2, 2008 at 3:46 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> > On Fri, 29 Aug 2008 16:38:24 -0500
> > Bob Tracy <rct@...rkin.frus.com> wrote:
> >
> >> With 2.6.27-rc4 and possibly earlier kernels, I see the following:
> >>
> >> $ cat /proc/mtrr
> >> cat: /proc/mtrr: Input/output error
> >>
> >> Processor is an AMD K6-III/450.
> >>
> >
> > static int mtrr_open(struct inode *inode, struct file *file)
> > {
> >        if (!mtrr_if)
> >                return -EIO;
> >
> >
> >
> > Beats me.  Perhaps something broke in mtrr_bp_init().
> >
> > It would be useful to know if 2.6.26 worked OK.
> >
> 
> two patches needed..
> 
> http://lkml.org/lkml/2008/9/1/307
>    [PATCH 4/6] x86: delay early cpu initialization until cpuid is done
> http://lkml.org/lkml/2008/9/1/308
>   [PATCH 5/6] x86: move mtrr cpu cap setting early in early_init_xxxx

Krzysztof Helt's quick-and-dirty patch posted a few days ago did the
trick, but from the descriptions of the above patches, they address the
problem properly.  Here's what "cat /proc/mtrr" shows with Helt's patch
and the "nv" driver active for my GeForce2 MX 400 card:

$ cat /proc/mtrr
reg00: base=0xd0000000 (3328MB), size=  64MB: write-combining, count=1

MTRR sanitization seems to be working properly: the same command shows
nothing when X isn't running.

-- 
------------------------------------------------------------------------
Bob Tracy          |  "I was a beta tester for dirt.  They never did
rct@...s.com       |   get all the bugs out." - Steve McGrew on /.
------------------------------------------------------------------------
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