linux-kernel - Re: [PATCH - resend] Memory-Hotplug: Fix the bug on interface /dev/mem for 64-bit kernel(v1)

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Message-ID: <20100112133556.GB7647@localhost>
Date:	Tue, 12 Jan 2010 21:35:56 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"Zheng, Shaohui" <shaohui.zheng@...el.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"y-goto@...fujitsu.com" <y-goto@...fujitsu.com>,
	Dave Hansen <haveblue@...ibm.com>,
	"x86@...nel.org" <x86@...nel.org>, Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH - resend] Memory-Hotplug: Fix the bug on interface
	/dev/mem for 64-bit kernel(v1)

On Tue, Jan 12, 2010 at 10:39:03AM +0800, KAMEZAWA Hiroyuki wrote:
> On Tue, 12 Jan 2010 10:33:08 +0800
> Wu Fengguang <fengguang.wu@...el.com> wrote:
> 
> > Sure, here it is :)
> > ---
> > x86: use the generic page_is_ram()
> > 
> > The generic resource based page_is_ram() works better with memory
> > hotplug/hotremove. So switch the x86 e820map based code to it.
> > 
> > CC: Andi Kleen <andi@...stfloor.org> 
> > CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> 
> > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> 
> Ack.

Thank you.

> 
> > +#ifdef CONFIG_X86
> > +	/*
> > +	 * A special case is the first 4Kb of memory;
> > +	 * This is a BIOS owned area, not kernel ram, but generally
> > +	 * not listed as such in the E820 table.
> > +	 */
> > +	if (pfn == 0)
> > +		return 0;
> > +
> > +	/*
> > +	 * Second special case: Some BIOSen report the PC BIOS
> > +	 * area (640->1Mb) as ram even though it is not.
> > +	 */
> > +	if (pfn >= (BIOS_BEGIN >> PAGE_SHIFT) &&
> > +	    pfn <  (BIOS_END   >> PAGE_SHIFT))
> > +		return 0;
> > +#endif
> 
> I'm glad if this part is sorted out in clean way ;)

Two possible solutions are:

- to exclude the above two ranges directly in e820 map;
- to not add the above two ranges into iomem_resource. 

Yinghai, do you have any suggestions?
We want to get rid of the two explicit tests from page_is_ram().

Thanks,
Fengguang

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