linux-kernel - Re: [PATCH 10/28] i386: map enough initial memory to create lowmem mappings

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Message-ID: <462CE1E0.9060007@zytor.com>
Date:	Mon, 23 Apr 2007 09:42:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Chuck Ebbert <cebbert@...hat.com>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	virtualization@...ts.osdl.org, lkml <linux-kernel@...r.kernel.org>,
	Zachary Amsden <zach@...are.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 10/28] i386: map enough initial memory to create lowmem
 mappings

Jeremy Fitzhardinge wrote:
> Eric W. Biederman wrote:
>> The only way to ensure this will not happen is to do what we do
>> on x86_64 and map the new page table page into our address space
>> before we write to it.  Assuming the page we allocate is already
>> mapped is simply not robust.
>>   
> 
> So you mean make alloc_bootmem make sure there's a mapping for the
> returned page?  That would be simple enough, though it might interact
> strangely with the actual construction of the memory mappings (what if
> the page alloc_bootmem just allocated for the pagetable is the page
> pagetable_init is actually trying to map?).
> 
> I'm not sure about the issue with holes.  I assume you mean that just
> because head.S maps a chunk of memory, it isn't necessarily available
> for allocation because its a hole.  But does alloc_bootmem know to avoid
> them anyway?  Has it already parsed e820 at that point?
> 

Since we allocate the maximum possible memory statically, I fail to see 
how holes could make the situation any worse, or better.

	-hpa
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