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

Chuck Ebbert
2007-04-19T20:48:18Z

Jeremy Fitzhardinge wrote:
> head.S creates the very initial pagetable for the kernel. This just
> maps enough space for the kernel itself, and an allocation bitmap.
> The amount of mapped memory is rounded up to 4Mbytes, and so this
> typically ends up mapping 8Mbytes of memory.
>
> When booting, pagetable_init() needs to create mappings for all
> lowmem, and the pagetables for these mappings are allocated from the
> free pages around the kernel in low memory. If the number of
> pagetable pages + kernel size exceeds head.S's initial mapping, it
> will end up faulting on an unmapped page. This will only happen with
> specific combinations of kernel size and memory size.
>
> This patch makes sure that head.S also maps enough space to fit the
> kernel pagetables as well as the kernel itself. It ends up using an
> additional two pages of unreclaimable memory.
>
> Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
> Acked-by: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Andi Kleen <ak@suse.de>
> Cc: Zachary Amsden <zach@vmware.com>
> Cc: Chris Wright <chrisw@sous-sol.org>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>,

Is some version of this going in for 2.6.21, or is it not a real problem?