Re: Crash while mapping memory in pagetable_init() (Was: Re: .config)

[Chris Wright <chrisw@sous-sol.org>]

* Jeremy Fitzhardinge (jeremy@goop.org) wrote:
> Subject: i386: map enough initial memory to create lowmem mappings
> 
> 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.

Yup, fixes it up here, nice catch.

Acked-by: Chris Wright <chrisw@sous-sol.org>