linux-kernel - Re: [Bug Fix]: Do 32-bit table calculations in pre-processor

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Message-ID: <4A4E58AC.7010905@zytor.com>
Date:	Fri, 03 Jul 2009 12:14:52 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	lkml@...ethan.org
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [Bug Fix]: Do 32-bit table calculations in pre-processor

Michael S. Zick wrote:
>>
>> The PGTABLE reservation seems much too big.  I think 1 page should be
>> sufficient for a system with large pages.  Even if not, 0x6d000 is way
>> too large.  And they symptoms of failing to reserve the initial
>> pagetable are pretty non-subtle.
>>
> 
> Random system halts, deadlocks with interrupts disabled?
> Yup, that sounds familiar.
> 
> If I ever get more than a stopped machine with a glowing power light;
> I will be certain to share.
> 

Let's see... on a non-PSE system we may need one PDE and one PTE page
per 4 MB, up to 1 GB, for a total of 256 pages or 1 MB of memory, so in
that sense 0x6d000 (109 pages) doesn't sound at all unreasonable
(non-PSE system with 512 MB of RAM?)

However, we shouldn't have to do this kind of hacks with
MAPPING_BEYOND_END, and we *certainly* shouldn't do it by implicitly
hard-coding the value of PAGE_SHIFT.

	-hpa

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

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