linux-kernel - Re: BUG: unable to handle kernel paging request at ffff8800cf669000

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Message-ID: <AANLkTinRCu1FuOYExo3cgNT=99gPkEZX8SvHWb6ux-bR@mail.gmail.com>
Date:	Mon, 17 Jan 2011 12:11:59 -0700
From:	xing lin <linxingnku@...il.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: BUG: unable to handle kernel paging request at ffff8800cf669000

On Mon, Jan 17, 2011 at 12:00 AM, Américo Wang <xiyou.wangcong@...il.com> wrote:
> If you are using x86, you have CONFIG_X86_PTDUMP, with which
> you can dump all page tables via debugfs.

It turns out CONFIG_X86_PTDUMP is not set. :-)
utos@...e:/boot$ grep PTDUMP /boot/config-2.6.32-24-generic
# CONFIG_X86_PTDUMP is not set
utos@...e:/boot$ uname -a
Linux node.memcached.checkpoint.emulab.net 2.6.32-24-generic
#38+emulab1 SMP Mon Aug 23 18:07:24 MDT 2010 x86_64 GNU/Linux

On the other hand, I do not understand why I need to look into page
tables. I think for the current 64-bit machines, all the physical
memory can be direct-mapped into the kernel logical space. In the AMD
64-bit machine, the kernel space ranges from [0xFFFF 8000 0000 0000,
0xFFFF FFFF FFFF FFFF] which is 128TB. In my Intel 64-bit machine, the
kernel is mapped at 0xFFFF 8800 0000 0000. I think the kernel space is
from [0xFFFF 8800 0000 0000, 0xFFFF FFFF FFFF FFFF] which is 119TB. So
I can use __pa() or __va() to get physical address or virtual address
directly. Right?

-- 
Regards,
Xing
School of Computing, University of Utah
http://www.cs.utah.edu/~xinglin/
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