[Intel-gfx] [PATCH 1/2] drm/i915: clear the shadow batch

[Chris Wilson]

Quoting Matthew Auld (2020-12-24 14:34:54)
> The shadow batch is an internal object, which doesn't have any page
> clearing, and since the batch_len can be smaller than the object, we
> should take care to clear it.
> 
> Testcase: igt/gen9_exec_parse/shadow-peek
> Fixes: 4f7af1948abc ("drm/i915: Support ro ppgtt mapped cmdparser shadow buffers")
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_cmd_parser.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_cmd_parser.c b/drivers/gpu/drm/i915/i915_cmd_parser.c
> index 8d88402387bd..ff3a0b8ccdd5 100644
> --- a/drivers/gpu/drm/i915/i915_cmd_parser.c
> +++ b/drivers/gpu/drm/i915/i915_cmd_parser.c
> @@ -1147,6 +1147,13 @@ static u32 *copy_batch(struct drm_i915_gem_object *dst_obj,
>         if (IS_ERR(dst))
>                 return dst;
>  
> +       if (length < dst_obj->base.size) {
> +               memset32(dst + length, 0,
> +                        (dst_obj->base.size - length) / sizeof(u32));
> +               __i915_gem_object_flush_map(dst_obj, length,
> +                                           dst_obj->base.size - length);
> +       }

I feel like we might as well remove the shadow_needs_clflush() and just
do a i915_gem_object_flush_map(shadow->obj) after parsing.

Then for simple chronological ordering, we can place this at the end of
copy_batch

memset32(dst + length, 0, (dst_obj->base.size - length) / sizeof(u32));

The cost of one more function call along here? Unnoticable.
-Chris