Re: [Intel-gfx] [PATCH v3 09/12] drm/ttm: Document and optimize ttm_bo_pipeline_gutting()

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On Fri, 21 May 2021 at 16:33, Thomas Hellström
<thomas.hellstrom@xxxxxxxxxxxxxxx> wrote:
>
> If the bo is idle when calling ttm_bo_pipeline_gutting(), we unnecessarily
> create a ghost object and push it out to delayed destroy.
> Fix this by adding a path for idle, and document the function.
>
> Also avoid having the bo end up in a bad state vulnerable to user-space
> triggered kernel BUGs if the call to ttm_tt_create() fails.
>
> Finally reuse ttm_bo_pipeline_gutting() in ttm_bo_evict().
>
> Cc: Christian König <christian.koenig@xxxxxxx>
> Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/ttm/ttm_bo.c      | 20 ++++++------
>  drivers/gpu/drm/ttm/ttm_bo_util.c | 52 ++++++++++++++++++++++++++++---
>  drivers/gpu/drm/ttm/ttm_tt.c      |  5 +++
>  include/drm/ttm/ttm_tt.h          | 10 ++++++
>  4 files changed, 73 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index ca1b098b6a56..a8fa3375b8aa 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -501,10 +501,15 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo,
>         bdev->funcs->evict_flags(bo, &placement);
>
>         if (!placement.num_placement && !placement.num_busy_placement) {
> -               ttm_bo_wait(bo, false, false);
> +               ret = ttm_bo_wait(bo, true, false);
> +               if (ret)
> +                       return ret;
>
> -               ttm_bo_cleanup_memtype_use(bo);
> -               return ttm_tt_create(bo, false);
> +               /*
> +                * Since we've already synced, this frees backing store
> +                * immediately.
> +                */
> +               return ttm_bo_pipeline_gutting(bo);
>         }
>
>         ret = ttm_bo_mem_space(bo, &placement, &evict_mem, ctx);
> @@ -974,13 +979,8 @@ int ttm_bo_validate(struct ttm_buffer_object *bo,
>         /*
>          * Remove the backing store if no placement is given.
>          */
> -       if (!placement->num_placement && !placement->num_busy_placement) {
> -               ret = ttm_bo_pipeline_gutting(bo);
> -               if (ret)
> -                       return ret;
> -
> -               return ttm_tt_create(bo, false);
> -       }
> +       if (!placement->num_placement && !placement->num_busy_placement)
> +               return ttm_bo_pipeline_gutting(bo);
>
>         /*
>          * Check whether we need to move buffer.
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> index 4a7d3d672f9a..7fa9b3a852eb 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> @@ -585,26 +585,70 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
>  }
>  EXPORT_SYMBOL(ttm_bo_move_accel_cleanup);
>
> +/**
> + * ttm_bo_pipeline_gutting - purge the contents of a bo
> + * @bo: The buffer object
> + *
> + * Purge the contents of a bo, async if the bo is not idle.
> + * After a successful call, the bo is left unpopulated in
> + * system placement. The function may wait uninterruptible
> + * for idle on OOM.
> + *
> + * Return: 0 if successful, negative error code on failure.
> + */
>  int ttm_bo_pipeline_gutting(struct ttm_buffer_object *bo)
>  {
>         static const struct ttm_place sys_mem = { .mem_type = TTM_PL_SYSTEM };
>         struct ttm_buffer_object *ghost;
> +       struct ttm_tt *ttm;
>         int ret;
>
> -       ret = ttm_buffer_object_transfer(bo, &ghost);
> +       /* If already idle, no need for ghost object dance. */
> +       ret = ttm_bo_wait(bo, false, true);
> +       if (ret != -EBUSY) {
> +               if (!bo->ttm) {
> +                       ret = ttm_tt_create(bo, true);

Why do we now unconditionally add clearing? Below also.

> +                       if (ret)
> +                               return ret;
> +               } else {
> +                       ttm_tt_unpopulate(bo->bdev, bo->ttm);
> +                       if (bo->type == ttm_bo_type_device)
> +                               ttm_tt_mark_for_clear(bo->ttm);
> +               }
> +               ttm_resource_free(bo, &bo->mem);
> +               ttm_resource_alloc(bo, &sys_mem, &bo->mem);
> +
> +               return 0;
> +       }
> +
> +       /*
> +        * We need an unpopulated ttm_tt after giving our current one,
> +        * if any, to the ghost object. And we can't afford to fail
> +        * creating one *after* the operation.
> +        */
> +
> +       ttm = bo->ttm;
> +       bo->ttm = NULL;
> +       ret = ttm_tt_create(bo, true);
> +       swap(bo->ttm, ttm);
>         if (ret)
>                 return ret;
>
> +       ret = ttm_buffer_object_transfer(bo, &ghost);
> +       if (ret) {
> +               ttm_tt_destroy(bo->bdev, ttm);
> +               return ret;
> +       }
> +
>         ret = dma_resv_copy_fences(&ghost->base._resv, bo->base.resv);
>         /* Last resort, wait for the BO to be idle when we are OOM */
>         if (ret)
>                 ttm_bo_wait(bo, false, false);
>
> -       ttm_resource_alloc(bo, &sys_mem, &bo->mem);
> -       bo->ttm = NULL;
> -
>         dma_resv_unlock(&ghost->base._resv);
>         ttm_bo_put(ghost);
> +       bo->ttm = ttm;
> +       ttm_resource_alloc(bo, &sys_mem, &bo->mem);
>
>         return 0;
>  }
> diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> index 0e41227116b1..913b330a234b 100644
> --- a/drivers/gpu/drm/ttm/ttm_tt.c
> +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> @@ -134,6 +134,11 @@ void ttm_tt_destroy_common(struct ttm_device *bdev, struct ttm_tt *ttm)
>  }
>  EXPORT_SYMBOL(ttm_tt_destroy_common);
>
> +void ttm_tt_mark_for_clear(struct ttm_tt *ttm)
> +{
> +       ttm->page_flags |= TTM_PAGE_FLAG_ZERO_ALLOC;
> +}
> +
>  void ttm_tt_destroy(struct ttm_device *bdev, struct ttm_tt *ttm)
>  {
>         bdev->funcs->ttm_tt_destroy(bdev, ttm);
> diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
> index 3102059db726..daa9c4cf48bb 100644
> --- a/include/drm/ttm/ttm_tt.h
> +++ b/include/drm/ttm/ttm_tt.h
> @@ -170,6 +170,16 @@ int ttm_tt_populate(struct ttm_device *bdev, struct ttm_tt *ttm, struct ttm_oper
>   */
>  void ttm_tt_unpopulate(struct ttm_device *bdev, struct ttm_tt *ttm);
>
> +/**
> + * ttm_tt_mark_for_clear - Mark pages for clearing on populate.
> + *
> + * @ttm: Pointer to the ttm_tt structure
> + *
> + * Marks pages for clearing so that the next time the page vector is
> + * populated, the pages will be cleared.
> + */
> +void ttm_tt_mark_for_clear(struct ttm_tt *ttm);
> +
>  void ttm_tt_mgr_init(unsigned long num_pages, unsigned long num_dma32_pages);
>
>  struct ttm_kmap_iter *ttm_kmap_iter_tt_init(struct ttm_kmap_iter_tt *iter_tt,
> --
> 2.31.1
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx




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