[PATCH 05/12] drm/ttm: convert page allocation to use page ptr array instead of list V3

[Jerome Glisse]

On Tue, Nov 08, 2011 at 09:11:20AM +0100, Thomas Hellstrom wrote:
> On 11/08/2011 12:40 AM, j.glisse at gmail.com wrote:
> >From: Jerome Glisse<jglisse at redhat.com>
> >
> >Use the ttm_tt page ptr array for page allocation, move the list to
> >array unwinding into the page allocation functions.
> >
> >V2 split the fix to use ttm put page as a separate fix
> >properly fill pages array when TTM_PAGE_FLAG_ZERO_ALLOC is not
> >set
> >V3 Added back page_count()==1 check when freeing page
> 
> NAK, this patch introduces a DOS vulnerability. It's allowing an
> arbitrary number of pages to be
> allocated *before* accounting them. Currently TTM is allowing a
> "small" (page size) memory size to be allocated before accounting.
> So page allocation must be interleaved with accounting on a per-page
> basis unless we can figure out a way to do the accounting *before*
> allocating the pages.
> 
> /Thomas
> 

Just a side note, current ttm_memory code is very likely to
loop forever in the kernel (so is DOS compliant too). It will
happen it ttm_shrink never succeed at freeing anythings which
is not unreliable.

Anyway i am doing a reserve/alloc_pages approach this will
more or less follow what current code does.

Cheers,
Jerome