linux-kernel - Re: [PATCH UPDATED] x86: set PAE PHYSICAL_MASK

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Date:	Tue, 10 Jun 2008 14:06:37 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jan Beulich <jbeulich@...ell.com>,
	Stable Kernel <stable@...nel.org>, x86@...nel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH UPDATED] x86: set PAE PHYSICAL_MASK_SHIFT to 44 bits.

Ingo Molnar wrote:
>> When a 64-bit x86 processor runs in 32-bit PAE mode, a pte can 
>> potentially have the same number of physical address bits as the 
>> 64-bit host ("Enhanced Legacy PAE Paging").  This means, in theory, we 
>> could have up to 52 bits of physical address in a pte.
>>
>> The 32-bit kernel uses a 32-bit unsigned long to represent a pfn. This 
>> means that it can only represent physical addresses up to 32+12=44 
>> bits wide.  Rather than widening pfns everywhere, just set 2^44 as the 
>> Linux x86_32-PAE architectural limit for physical address size.
>>     
>
> applied to tip/x86/cleanups - thanks Jeremy. No urgency for v2.6.26, 
> right?

Not urgent, but it would be nice to have.

    J

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