Re: [Intel-gfx] [RFC PATCH 02/16] drm/ttm/pool: Fix ttm_pool_alloc error path

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Wed, 2023-02-15 at 18:31 +0100, Christian König wrote:
> Am 15.02.23 um 17:13 schrieb Thomas Hellström:
> > When hitting an error, the error path forgot to unmap dma mappings
> > and
> 
> I don't see where this happens?

From what I can tell, ttm_pool_page_allocated() maps the page for dma,
If we later hit an error, ttm_pool_free_page() will leak the mapping.

> 
> > could call set_pages_wb() on already uncached pages.
> 
> Yeah, but what's the problem?

Umm, at least if you try to set WC on an already WC'd page, the
set_pages_ code will spam dmesg with warnings. 
Not sure if set_pages_wb() on WB pages does the same, nor if it
issues unnecessary global cache / tlb flushes or whether that will
change in the future.
The point of avoiding the set_pages_wb() when already WB is you don't
have to check, and you don't have to care.

That said, the __ttm_pool_free() is used also in upcoming patches.

/Thomas


> 
> Regards,
> Christian.
> 
> > 
> > Fix this by introducing a common __ttm_pool_free() function that
> > does the right thing.
> > 
> > Fixes: d099fc8f540a ("drm/ttm: new TT backend allocation pool v3")
> > Cc: Christian König <christian.koenig@amd.com>
> > Cc: Dave Airlie <airlied@redhat.com>
> > Cc: Madhav Chauhan <madhav.chauhan@amd.com>
> > Cc: Christian Koenig <christian.koenig@amd.com>
> > Cc: Huang Rui <ray.huang@amd.com>
> > Cc: dri-devel@lists.freedesktop.org
> > Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > ---
> >   drivers/gpu/drm/ttm/ttm_pool.c | 74 +++++++++++++++++++++--------
> > -----
> >   1 file changed, 45 insertions(+), 29 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/ttm/ttm_pool.c
> > b/drivers/gpu/drm/ttm/ttm_pool.c
> > index aa116a7bbae3..1cc7591a9542 100644
> > --- a/drivers/gpu/drm/ttm/ttm_pool.c
> > +++ b/drivers/gpu/drm/ttm/ttm_pool.c
> > @@ -367,6 +367,39 @@ static int ttm_pool_page_allocated(struct
> > ttm_pool *pool, unsigned int order,
> >         return 0;
> >   }
> >   
> > +static void __ttm_pool_free(struct ttm_pool *pool, struct ttm_tt
> > *tt,
> > +                           struct page **caching_divide,
> > +                           enum ttm_caching initial_caching,
> > +                           enum ttm_caching subseq_caching,
> > +                           pgoff_t num_pages)
> > +{
> > +       enum ttm_caching caching = subseq_caching;
> > +       struct page **pages = tt->pages;
> > +       unsigned int order;
> > +       pgoff_t i, nr;
> > +
> > +       if (pool && caching_divide)
> > +               caching = initial_caching;
> > +
> > +       for (i = 0; i < num_pages; i += nr, pages += nr) {
> > +               struct ttm_pool_type *pt = NULL;
> > +
> > +               if (unlikely(caching_divide == pages))
> > +                       caching = subseq_caching;
> > +
> > +               order = ttm_pool_page_order(pool, *pages);
> > +               nr = (1UL << order);
> > +               if (tt->dma_address)
> > +                       ttm_pool_unmap(pool, tt->dma_address[i],
> > nr);
> > +
> > +               pt = ttm_pool_select_type(pool, caching, order);
> > +               if (pt)
> > +                       ttm_pool_type_give(pt, *pages);
> > +               else
> > +                       ttm_pool_free_page(pool, caching, order,
> > *pages);
> > +       }
> > +}
> > +
> >   /**
> >    * ttm_pool_alloc - Fill a ttm_tt object
> >    *
> > @@ -386,8 +419,9 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > struct ttm_tt *tt,
> >         dma_addr_t *dma_addr = tt->dma_address;
> >         struct page **caching = tt->pages;
> >         struct page **pages = tt->pages;
> > +       enum ttm_caching page_caching;
> >         gfp_t gfp_flags = GFP_USER;
> > -       unsigned int i, order;
> > +       unsigned int order;
> >         struct page *p;
> >         int r;
> >   
> > @@ -410,6 +444,7 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > struct ttm_tt *tt,
> >              order = min_t(unsigned int, order, __fls(num_pages)))
> > {
> >                 struct ttm_pool_type *pt;
> >   
> > +               page_caching = tt->caching;
> >                 pt = ttm_pool_select_type(pool, tt->caching,
> > order);
> >                 p = pt ? ttm_pool_type_take(pt) : NULL;
> >                 if (p) {
> > @@ -418,6 +453,7 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > struct ttm_tt *tt,
> >                         if (r)
> >                                 goto error_free_page;
> >   
> > +                       caching = pages;
> >                         do {
> >                                 r = ttm_pool_page_allocated(pool,
> > order, p,
> >                                                            
> > &dma_addr,
> > @@ -426,14 +462,15 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > struct ttm_tt *tt,
> >                                 if (r)
> >                                         goto error_free_page;
> >   
> > +                               caching = pages;
> >                                 if (num_pages < (1 << order))
> >                                         break;
> >   
> >                                 p = ttm_pool_type_take(pt);
> >                         } while (p);
> > -                       caching = pages;
> >                 }
> >   
> > +               page_caching = ttm_cached;
> >                 while (num_pages >= (1 << order) &&
> >                        (p = ttm_pool_alloc_page(pool, gfp_flags,
> > order))) {
> >   
> > @@ -442,6 +479,7 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > struct ttm_tt *tt,
> >                                                            tt-
> > >caching);
> >                                 if (r)
> >                                         goto error_free_page;
> > +                               caching = pages;
> >                         }
> >                         r = ttm_pool_page_allocated(pool, order, p,
> > &dma_addr,
> >                                                     &num_pages,
> > &pages);
> > @@ -468,15 +506,12 @@ int ttm_pool_alloc(struct ttm_pool *pool,
> > struct ttm_tt *tt,
> >         return 0;
> >   
> >   error_free_page:
> > -       ttm_pool_free_page(pool, tt->caching, order, p);
> > +       ttm_pool_free_page(pool, page_caching, order, p);
> >   
> >   error_free_all:
> >         num_pages = tt->num_pages - num_pages;
> > -       for (i = 0; i < num_pages; ) {
> > -               order = ttm_pool_page_order(pool, tt->pages[i]);
> > -               ttm_pool_free_page(pool, tt->caching, order, tt-
> > >pages[i]);
> > -               i += 1 << order;
> > -       }
> > +       __ttm_pool_free(pool, tt, caching, tt->caching, ttm_cached,
> > +                       num_pages);
> >   
> >         return r;
> >   }
> > @@ -492,27 +527,8 @@ EXPORT_SYMBOL(ttm_pool_alloc);
> >    */
> >   void ttm_pool_free(struct ttm_pool *pool, struct ttm_tt *tt)
> >   {
> > -       unsigned int i;
> > -
> > -       for (i = 0; i < tt->num_pages; ) {
> > -               struct page *p = tt->pages[i];
> > -               unsigned int order, num_pages;
> > -               struct ttm_pool_type *pt;
> > -
> > -               order = ttm_pool_page_order(pool, p);
> > -               num_pages = 1ULL << order;
> > -               if (tt->dma_address)
> > -                       ttm_pool_unmap(pool, tt->dma_address[i],
> > num_pages);
> > -
> > -               pt = ttm_pool_select_type(pool, tt->caching,
> > order);
> > -               if (pt)
> > -                       ttm_pool_type_give(pt, tt->pages[i]);
> > -               else
> > -                       ttm_pool_free_page(pool, tt->caching,
> > order,
> > -                                          tt->pages[i]);
> > -
> > -               i += num_pages;
> > -       }
> > +       __ttm_pool_free(pool, tt, NULL, tt->caching, tt->caching,
> > +                       tt->num_pages);
> >   
> >         while (atomic_long_read(&allocated_pages) > page_pool_size)
> >                 ttm_pool_shrink();
>