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

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Date:	Fri, 18 Jun 2010 09:32:37 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	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
Subject: Re: [PATCH 1/2] x86: ioremap: fix wrong physical address handling

(2010/06/17 22:46), H. Peter Anvin wrote:
> On 06/17/2010 02:35 AM, Jeremy Fitzhardinge wrote:
>>>>
>>>> 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?
>>
>> That's an awkward situation.  I would tend to suggest that you not
>> support this type of machine with a 32-bit kernel.  Is it a sparse
>> memory system, or is there a device mapped in that range?
>>
>> I guess it would be possible to special-case ioremap to allow the
>> creation of such mappings, but I don't know what kind of system-wide
>> fallout would happen as a result.  The consequences of something trying
>> to extract a pfn from one of those ptes would be
>>
>>> 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.)
>>>
>>
>> There are many places which hold pfns in 32 bit variables on 32 bit
>> systems; the standard type for pfns is "unsigned long", pretty much
>> everywhere in the kernel.  It might be worth defining a pfn_t and
>> converting usage over to that, but it would be a pervasive change.
>>
>
> I think you're right, and just making 2^44 work correctly would be good
> enough.  Doing special forwarding of all 52 bits of the real physical
> address in the paravirt case (where it is self-contained and doesn't
> spill into the rest of the kernel) would probably be a good thing, though.
>
> 	-hpa
>

I'll focus on making 2^44 work correctly. Then, I'll do the following
change in the next version of my patch.

- The v.2 patch uses resource_size_t for pfn. I'll keep using
   resource_size_t for pfn also in v.3, because there is no reason to
   leave it being "unsigned long".

- Use PHYSICAL_PAGE_MASK for masking physical address as v.1 patch
   did. I think changing the definition of PAGE_MASK is a little risky.

Thanks,
Kenji Kaneshige


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