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

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Message-ID: <20080610103151.GG19136@elte.hu>
Date:	Tue, 10 Jun 2008 12:31:51 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
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.


* Jeremy Fitzhardinge <jeremy@...p.org> 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?

	Ingo
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