Re: early fixmap causes kmap breakage

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 18 Dec 2008 22:15:43 +0100
Nick Piggin <npiggin@suse.de> wrote:

> Hi,
> 
> I've debugged a problem where i386+pae systems with more than a few CPUs
> blow up at boot in the kmap_atomic code.

ping?

> The problem is that the kmap_atomic pte pages all need to be contiguous
> memory because the pte is calculated via the first kmap pte page + an
> offset (so as not to have to walk the page tables every time).
> 
> The fixmap setup code crudely allocates contiguous pte pages, which is fine,
> but if it finds an already populated pmd entry, then it will not switch it
> to a new, contiguous pte page. So the early fixmap introduces a discontig
> page table right in the middle of the kmap atomic fixmaps.
> 
> Commenting out the eaarly fixmap setup in head_32.S gets everything working
> properly. What would be the best way to fix this? Could we put the early
> fixmap page table in initdata, and then have the fixmap setup proper first
> clear its corresponding pmd entry?

How come users/testers aren't reporting this?