Re: [PATCH 3/4] drm/amdgpu: add independent DMA-buf export v3

["Zhang, Jerry (Junwei)" <Jerry.Zhang@amd.com>]

On 06/22/2018 10:11 PM, Christian König wrote:
> The caching of SGT's done by the DRM code is actually quite harmful and
> should probably removed altogether in the long term.
>
> Start by providing a separate DMA-buf export implementation in amdgpu. This is
> also a prerequisite of unpinned DMA-buf handling.
>
> v2: fix unintended recursion, remove debugging leftovers
> v3: split out from unpinned DMA-buf work
>
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu.h       |  1 -
>   drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c   |  1 -
>   drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c | 94 +++++++++++++------------------
>   3 files changed, 39 insertions(+), 57 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> index d8e0cc08f9db..5e71af8dd3a7 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> @@ -373,7 +373,6 @@ int amdgpu_gem_object_open(struct drm_gem_object *obj,
>   void amdgpu_gem_object_close(struct drm_gem_object *obj,
>   				struct drm_file *file_priv);
>   unsigned long amdgpu_gem_timeout(uint64_t timeout_ns);
> -struct sg_table *amdgpu_gem_prime_get_sg_table(struct drm_gem_object *obj);
>   struct drm_gem_object *
>   amdgpu_gem_prime_import_sg_table(struct drm_device *dev,
>   				 struct dma_buf_attachment *attach,
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> index a549483032b0..cdf0be85d361 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> @@ -919,7 +919,6 @@ static struct drm_driver kms_driver = {
>   	.gem_prime_export = amdgpu_gem_prime_export,
>   	.gem_prime_import = amdgpu_gem_prime_import,
>   	.gem_prime_res_obj = amdgpu_gem_prime_res_obj,
> -	.gem_prime_get_sg_table = amdgpu_gem_prime_get_sg_table,

I may miss some patches or important info.

Even applied the series of patch, I still could find below code in drm_gem_map_dma_buf().
In this case, it will cause NULL pointer access. Please help me out of here.
{{{
sgt = obj->dev->driver->gem_prime_get_sg_table(obj);
}}}

Jerry

>   	.gem_prime_import_sg_table = amdgpu_gem_prime_import_sg_table,
>   	.gem_prime_vmap = amdgpu_gem_prime_vmap,
>   	.gem_prime_vunmap = amdgpu_gem_prime_vunmap,
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c
> index b2286bc41aec..038a8c8488b7 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_prime.c
> @@ -40,22 +40,6 @@
>
>   static const struct dma_buf_ops amdgpu_dmabuf_ops;
>
> -/**
> - * amdgpu_gem_prime_get_sg_table - &drm_driver.gem_prime_get_sg_table
> - * implementation
> - * @obj: GEM buffer object
> - *
> - * Returns:
> - * A scatter/gather table for the pinned pages of the buffer object's memory.
> - */
> -struct sg_table *amdgpu_gem_prime_get_sg_table(struct drm_gem_object *obj)
> -{
> -	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
> -	int npages = bo->tbo.num_pages;
> -
> -	return drm_prime_pages_to_sg(bo->tbo.ttm->pages, npages);
> -}
> -
>   /**
>    * amdgpu_gem_prime_vmap - &dma_buf_ops.vmap implementation
>    * @obj: GEM buffer object
> @@ -189,35 +173,29 @@ amdgpu_gem_prime_import_sg_table(struct drm_device *dev,
>   }
>
>   /**
> - * amdgpu_gem_map_attach - &dma_buf_ops.attach implementation
> - * @dma_buf: shared DMA buffer
> - * @target_dev: target device
> + * amdgpu_gem_map_dma_buf - &dma_buf_ops.map_dma_buf implementation
>    * @attach: DMA-buf attachment
> + * @dir: DMA direction
>    *
>    * Makes sure that the shared DMA buffer can be accessed by the target device.
>    * For now, simply pins it to the GTT domain, where it should be accessible by
>    * all DMA devices.
>    *
>    * Returns:
> - * 0 on success or negative error code.
> + * sg_table filled with the DMA addresses to use or ERR_PRT with negative error
> + * code.
>    */
> -static int amdgpu_gem_map_attach(struct dma_buf *dma_buf,
> -				 struct dma_buf_attachment *attach)
> +static struct sg_table *
> +amdgpu_gem_map_dma_buf(struct dma_buf_attachment *attach,
> +		       enum dma_data_direction dir)
>   {
> +	struct dma_buf *dma_buf = attach->dmabuf;
>   	struct drm_gem_object *obj = dma_buf->priv;
>   	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
>   	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
> +	struct sg_table *sgt;
>   	long r;
>
> -	r = drm_gem_map_attach(dma_buf, attach);
> -	if (r)
> -		return r;
> -
> -	r = amdgpu_bo_reserve(bo, false);
> -	if (unlikely(r != 0))
> -		goto error_detach;
> -
> -
>   	if (attach->dev->driver != adev->dev->driver) {
>   		/*
>   		 * Wait for all shared fences to complete before we switch to future
> @@ -228,54 +206,62 @@ static int amdgpu_gem_map_attach(struct dma_buf *dma_buf,
>   							MAX_SCHEDULE_TIMEOUT);
>   		if (unlikely(r < 0)) {
>   			DRM_DEBUG_PRIME("Fence wait failed: %li\n", r);
> -			goto error_unreserve;
> +			return ERR_PTR(r);
>   		}
>   	}
>
>   	/* pin buffer into GTT */
>   	r = amdgpu_bo_pin(bo, AMDGPU_GEM_DOMAIN_GTT, NULL);
>   	if (r)
> -		goto error_unreserve;
> +		return ERR_PTR(r);
> +
> +	sgt = drm_prime_pages_to_sg(bo->tbo.ttm->pages, bo->tbo.num_pages);
> +	if (IS_ERR(sgt))
> +		return sgt;
> +
> +	if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
> +			      DMA_ATTR_SKIP_CPU_SYNC))
> +		goto error_free;
>
>   	if (attach->dev->driver != adev->dev->driver)
>   		bo->prime_shared_count++;
>
> -error_unreserve:
> -	amdgpu_bo_unreserve(bo);
> +	return sgt;
>
> -error_detach:
> -	if (r)
> -		drm_gem_map_detach(dma_buf, attach);
> -	return r;
> +error_free:
> +	sg_free_table(sgt);
> +	kfree(sgt);
> +	return ERR_PTR(-ENOMEM);
>   }
>
>   /**
> - * amdgpu_gem_map_detach - &dma_buf_ops.detach implementation
> - * @dma_buf: shared DMA buffer
> + * amdgpu_gem_unmap_dma_buf - &dma_buf_ops.unmap_dma_buf implementation
>    * @attach: DMA-buf attachment
> + * @sgt: sg_table to unmap
> + * @dir: DMA direction
>    *
>    * This is called when a shared DMA buffer no longer needs to be accessible by
>    * the other device. For now, simply unpins the buffer from GTT.
>    */
> -static void amdgpu_gem_map_detach(struct dma_buf *dma_buf,
> -				  struct dma_buf_attachment *attach)
> +static void amdgpu_gem_unmap_dma_buf(struct dma_buf_attachment *attach,
> +				     struct sg_table *sgt,
> +				     enum dma_data_direction dir)
>   {
> +	struct dma_buf *dma_buf = attach->dmabuf;
>   	struct drm_gem_object *obj = dma_buf->priv;
>   	struct amdgpu_bo *bo = gem_to_amdgpu_bo(obj);
>   	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
> -	int ret = 0;
> -
> -	ret = amdgpu_bo_reserve(bo, true);
> -	if (unlikely(ret != 0))
> -		goto error;
>
>   	amdgpu_bo_unpin(bo);
> +
>   	if (attach->dev->driver != adev->dev->driver && bo->prime_shared_count)
>   		bo->prime_shared_count--;
> -	amdgpu_bo_unreserve(bo);
>
> -error:
> -	drm_gem_map_detach(dma_buf, attach);
> +	if (sgt) {
> +		dma_unmap_sg(attach->dev, sgt->sgl, sgt->nents, dir);
> +		sg_free_table(sgt);
> +		kfree(sgt);
> +	}
>   }
>
>   /**
> @@ -333,10 +319,8 @@ static int amdgpu_gem_begin_cpu_access(struct dma_buf *dma_buf,
>   }
>
>   static const struct dma_buf_ops amdgpu_dmabuf_ops = {
> -	.attach = amdgpu_gem_map_attach,
> -	.detach = amdgpu_gem_map_detach,
> -	.map_dma_buf = drm_gem_map_dma_buf,
> -	.unmap_dma_buf = drm_gem_unmap_dma_buf,
> +	.map_dma_buf = amdgpu_gem_map_dma_buf,
> +	.unmap_dma_buf = amdgpu_gem_unmap_dma_buf,
>   	.release = drm_gem_dmabuf_release,
>   	.begin_cpu_access = amdgpu_gem_begin_cpu_access,
>   	.map = drm_gem_dmabuf_kmap,
>
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