Re: [Intel-gfx] [PATCH 3/4] drm/i915/ttm: ensure we unmap when purging

Thomas Hellström
2022-01-05T15:28:30Z

On Wed, 2022-01-05 at 14:58 +0000, Matthew Auld wrote:
> Purging can happen during swapping out, or directly invoked with the
> madvise ioctl. In such cases this doesn't involve a ttm move, which
> skips umapping the object.
>
> Fixes: cf3e3e86d779 ("drm/i915: Use ttm mmap handling for ttm bo's.")
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> index 8d61d4538a64..f148e7e48f86 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> @@ -399,6 +399,8 @@ int i915_ttm_purge(struct drm_i915_gem_object
> *obj)
>         if (obj->mm.madv == __I915_MADV_PURGED)
>                 return 0;
>
> +       ttm_bo_unmap_virtual(bo);
> +
>         ret = ttm_bo_validate(bo, &place, &ctx);
>         if (ret)
>                 return ret;

The swap notifier and the move code both call i915_ttm_move_notify() to
achieve this before calling i915_ttm_purge. This ensures both cpu- and
gpu ptes are torn down, and also when we extend to dynamic dma-buf
exporting, makes sure dma-buf importers unbind.

So I suggest we make a i915_ttm_truncate wrapper function that calls
i915_ttm_move_notify() and then ttm_bo_purge(), and use that as the
truncate callback as well as from those places we call i915_ttm_purge
without a prior call to i915_ttm_move_notify(), which seems to be the
ones you've identified in patch 3 and 4,

/Thomas