linux-kernel - Re: [PATCH 1/2] x86: ioremap: fix wrong physical address handling

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Message-ID: <4C19BED5.4090801@jp.fujitsu.com>
Date:	Thu, 17 Jun 2010 15:21:09 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Matthew Wilcox <matthew@....cx>, tglx@...utronix.de,
	mingo@...hat.com, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, macro@...ux-mips.org,
	kamezawa.hiroyu@...fujitsu.com, eike-kernel@...tec.de,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH 1/2] x86: ioremap: fix wrong physical address handling

(2010/06/17 15:03), H. Peter Anvin wrote:
> On 06/16/2010 09:55 PM, Kenji Kaneshige wrote:
>>>
>>> I think they might be. Kenji?
>>
>> No. My addresses are in the 44-bits range (around fc000000000). So it is
>> not required for my problem. This change assumes that phys_addr can be
>> above 44-bits (up to 52-bits (and higher in the future?)).
>>
>> By the way, is there linux kernel limit regarding above 44-bits physical
>> address in x86_32 PAE? For example, pfn above 32-bits is not supported?
>>
>
> There are probably places at which PFNs are held in 32-bit numbers,
> although it would be good to track them down if it isn't too expensive
> to fix them (i.e. doesn't affect generic code.)
>
> This also affects paravirt systems, i.e. right now Xen has to locate all
> 32-bit guests below 64 GB, which limits its usefulness.
>
>> #ifdef CONFIG_X86_PAE
>> /* 44=32+12, the limit we can fit into an unsigned long pfn */
>> #define __PHYSICAL_MASK_SHIFT   44
>> #define __VIRTUAL_MASK_SHIFT    32
>>
>> If there is 44-bits physical address limit, I think it's better to use
>> PHYSICAL_PAGE_MASK for masking physical address, instead of "(phys_addr
>>>> PAGE_SHIFT)<<  PAGE_SHIFT)". The PHYSICAL_PAGE_MASK would become
>> greater value when 44-bits physical address limit is eliminated. And
>> maybe we need to change phys_addr_valid() returns error if physical
>> address is above (1<<  __PHYSICAL_MASK_SHIFT)?
>
> The real question is how much we can fix without an unreasonable cost.
>

Thank you very much. I understand the situation.

Thanks,
Kenji Kaneshige


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