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Date: Sun, 09 Sep 2012 13:33:38 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: David Woodhouse <dwmw2@infradead.org>
Subject: Re: mtd: kernel BUG at arch/x86/mm/pat.c:279!
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Cc: Suresh Siddha <suresh.b.siddha@intel.com>,
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On 09/09/2012 12:04 PM, David Woodhouse wrote:
> On Sun, 2012-09-09 at 09:56 -0700, H. Peter Anvin wrote:
>>
>>> So it should either be start=0xfffffffffffff000 end=0xffffffffffffffff
>>> or it should be start=0xfffffffffffff000 len=0x1000.
>>
>> I would strongly object to the former; that kind of inclusive ranges
>> breed a whole class of bugs by themselves.
>
> Another alternative that avoids overflow issues is to use a PFN rather
> than a byte address.
>

Except as a result of that logic have a bunch of places which either 
have rounding errors in how they calculate PFNs, or they think they can 
stick PFNs into 32-bit numbers.  :(

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.