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: <20100112093031.0fc6877f.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 12 Jan 2010 09:30:31 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Wu Fengguang <fengguang.wu@...el.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>
Subject: Re: [PATCH - resend] Memory-Hotplug: Fix the bug on interface
 /dev/mem for 64-bit kernel(v1)

On Mon, 11 Jan 2010 20:43:03 +0800
Wu Fengguang <fengguang.wu@...el.com> wrote:

> > > +	/* if add to low memory, update max_low_pfn */
> > > +	if (unlikely(start_pfn < limit_low_pfn)) {
> > > +		if (end_pfn <= limit_low_pfn)
> > > +			max_low_pfn = end_pfn;
> > > +		else
> > > +			max_low_pfn = limit_low_pfn;
> > 
> > X86_64 actually always set max_low_pfn=max_pfn, in setup_arch():
> > [Zheng, Shaohui] there should be some misunderstanding, I read the
> > code carefully, if the total memory is under 4G, it always
> > max_low_pfn=max_pfn. If the total memory is larger than 4G,
> > max_low_pfn means the end of low ram. It set
> 
> > max_low_pfn = e820_end_of_low_ram_pfn();.
> 
> The above line is very misleading.. In setup_arch(), it will be
> overrode by the following block.
> 

Hmmm....could you rewrite /dev/mem to use kernel/resource.c other than
modifing e820 maps. ?
Two reasons.
  - e820map is considerted to be stable, read-only after boot.
  - We don't need to add more x86 special codes.


Thanks,
-Kame

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