linux-kernel - Re: [PATCH 2/4] x86: ioremap: fix physical address check

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Message-ID: <4C164688.2030107@zytor.com>
Date:	Mon, 14 Jun 2010 08:11:04 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
CC:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, jbarnes@...tuousgeek.org
Subject: Re: [PATCH 2/4] x86: ioremap: fix physical address check

On 06/13/2010 11:38 PM, Maciej W. Rozycki wrote:
> On Mon, 14 Jun 2010, Kenji Kaneshige wrote:
> 
>> - Architectural limit of physical address in x86 32-bit mode is 40-bit
>>   (depnds on processor version).
> 
>  According to documentation I happen to have handy this limit is actually 
> 52 bits (and space is currently available in the data structures used for 
> a possible future extension up to 63 bits).
> 

Yes.  There are, however, very likely bugs in several classes due to
incorrect bitmasks as well as 32-bit PFNs.

We have made the decision based on data structure limitations (and just
usability) to not support more than 2^36 bytes of RAM on 32 bits, but
those data structures should not affect I/O.  I;d like to track down and
fix the bugs instead of papering over the problem...

	-hpa

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

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