linux-kernel - Re: [RFC BUG?] dereference PAGE

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Date:	Wed, 2 May 2007 10:52:20 -0700
From:	Bill Irwin <bill.irwin@...cle.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Bill Irwin <bill.irwin@...cle.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Kruchinin <dubalom@...il.com>,
	linux-kernel@...r.kernel.org,
	Jeremy Fitzhardinge <jeremy@...source.com>,
	Andi Kleen <ak@...e.de>, Ingo Molnar <mingo@...e.hu>,
	wli@...omorphy.com
Subject: Re: [RFC BUG?] dereference PAGE_OFFSET address (rc7-mm2)

On Wed, May 02, 2007 at 09:28:46AM -0700, Jeremy Fitzhardinge wrote:
>>> I think this should be fixed now.  Eric made all those writes
>>> unconditional (to fix a problem with PSE superpages not being created). 
>>> The patch is in Andi's queue.

Bill Irwin <bill.irwin@...cle.com> writes:
>> It needs verification with the testcase from this thread.

On Wed, May 02, 2007 at 11:16:27AM -0600, Eric W. Biederman wrote:
> Sounds reasonable.
> However there is no reason to suspect it won't fix this case because
> unconditional writes are what we have always done, and we have always
> kept swapper_pg_dir from early boot as well.
> In essence my patch I sent out to Andi was a partial revert.

It would not be so far out to be aware of what pagetable entries were
carried over from the initial swapper_pg_dir and explicitly clobber
them (for instance, modifying their protection bits while otherwise
retaining them).


On Wed, May 02, 2007 at 11:16:27AM -0600, Eric W. Biederman wrote:
> It isn't slated to go in until nextround but I also rewrote the early
> page table setup in C.  Allowing set_fixmap to work in the early
> kernel, and fix problems of not having enough memory mapped to build
> the identity mappings, because we are then updating the page table
> we have also in the PAE case.

I'm not sure when we run into those problems, though I understand what
they are. I suppose it would be good to resolve them.


-- wli
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