linux-kernel - Re: [PATCH] i386: For debugging, make the initial page table setup less forgiving.

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Message-ID: <4620038B.5020700@zytor.com>
Date:	Fri, 13 Apr 2007 15:26:19 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Zachary Amsden <zach@...are.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i386: For debugging, make the initial page table setup
 less forgiving.

Zachary Amsden wrote:
> H. Peter Anvin wrote:
>> +    /*
>> +     * End condition: we must map up to and including
>> +     * INIT_MAP_BEYOND_END bytes beyond the end of our
>> +     * own page tables; 0x1000 is the size of the page
>> +     * table were about to write, and +0x007 is the
>> +     * attribute bits.
>> +     */
>> +    leal (INIT_MAP_BEYOND_END+0x1000+0x007)(%edi),%ebp
>>   
> 
> hrmm?  Shouldn't that still be INIT_MAP_BEYOND_END+0x0007?  Seems you 
> are mapping 4M more than you need.
> 

4K, not 4M.  This is an actual address, not an indirection.

However, the expression is correct, because it needs to refer to the 
termination address *after* the current page table is written -- you can 
think of it as having already allocated 4K for a page table that it is 
about to be generated.

	-hpa

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