From: Andreas Schwab <schwab@linux-m68k.org>
To: Lanttor <lanttor.guo@freescale.com>
Cc: linux-m68k@vger.kernel.org
Subject: Re: why the PAGE_OFFSET is not 0xc0000000 on m68k platform
Date: Thu, 21 May 2009 13:29:44 +0200 [thread overview]
Message-ID: <m23aaylmmv.fsf@igel.home> (raw)
In-Reply-To: <4A14D5E5.9070103@freescale.com> (Lanttor's message of "Thu, 21 May 2009 12:17:41 +0800")
Lanttor <lanttor.guo@freescale.com> writes:
> In my understanding, the kernel page mapping depends on PAGE_OFFSET.
> For example, if PAGE_OFFSET is 0x00000000 (assuming 256M memory), the
> kernel virtual address will be at (0x00000000 - 0x10000000), right?
On m68k, the kernel virtual addresses are in a separate address space
from user space, thus the value of PAGE_OFFSET is somewhat arbitrary.
> Could this incur some side effect? I see the definition of PAGE_OFFSET
> is 0xc0000000 on much platforms.
On those platforms kernel and user space share the same address space,
and PAGE_OFFSET makes sure that they don't overlap.
Andreas.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
prev parent reply other threads:[~2009-05-21 11:29 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-21 4:17 why the PAGE_OFFSET is not 0xc0000000 on m68k platform Lanttor
2009-05-21 11:29 ` Andreas Schwab [this message]
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