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

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Message-Id: <200907031441.04604.lkml@morethan.org>
Date:	Fri, 3 Jul 2009 14:41:01 -0500
From:	"Michael S. Zick" <lkml@...ethan.org>
To:	"H. Peter Anvin" <hpa@...or.com>
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

On Fri July 3 2009, H. Peter Anvin wrote:
> 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.
> 

Good point: (1<<(32-PAGE_SIFT)) would handle other than 4k pages.

I just hardcoded it as a working example of the change from setting
the page table size by design rather than numeric error.

And yes, it has 512Mbyte of ram, so 1/2Mbyte page table sounds right to me.

Mike
> 	-hpa
> 


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