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

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Message-ID: <462CE027.4030302@goop.org>
Date:	Mon, 23 Apr 2007 09:34:47 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Chuck Ebbert <cebbert@...hat.com>,
	"H. Peter Anvin" <hpa@...or.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

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?

    J
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