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

[Wu Fengguang <fengguang.wu@intel.com>]

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@intel.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@firstfloor.org> 
> > CC: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> 
> > Signed-off-by: Wu Fengguang <fengguang.wu@intel.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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