[igt-dev] [PATCH i-g-t] lib: Only avoid relocations with full-ppgtt

[Zbigniew Kempczyński]

On Fri, Sep 25, 2020 at 09:41:48AM +0100, Chris Wilson wrote:
> We can only assigned random addresses with impunity if we know we have
> complete control over the ppGTT. If the ppGTT is shared, either aliased
> with the global GTT or simply the global GTT on ancient HW, then we have
> to be careful in case they are objects already fixed in place inside the
> GTT, e.g. active framebuffers. As the relocation code is still
> available, only enforce no-relocations by default when the context has
> its own ppGTT.
> 
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2491
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
> ---
>  lib/intel_batchbuffer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/intel_batchbuffer.c b/lib/intel_batchbuffer.c
> index be764646e..42d7cd251 100644
> --- a/lib/intel_batchbuffer.c
> +++ b/lib/intel_batchbuffer.c
> @@ -1306,7 +1306,7 @@ __intel_bb_create(int i915, uint32_t size, bool do_relocs)
>   */
>  struct intel_bb *intel_bb_create(int i915, uint32_t size)
>  {
> -	return __intel_bb_create(i915, size, false);
> +	return __intel_bb_create(i915, size, !gem_uses_full_ppgtt(i915));
>  }
>  
>  /**
> -- 
> 2.28.0

If we won't enforce EXEC_OBJECT_PINNED and set I915_EXEC_NO_RELOC for execbuf
still driver will try to use offsets configured in the objects array? I thought
NO_RELOC + !PINNED will relocate not properly configured objects but I'm likely
wrong. I don't have much experience with !ppgtt tables but if they are shared
I guess we can rely on kernel relocations only. So

Reviewed-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>