Re: [PATCH 04/12] dma-buf: add optional invalidate_mappings callback v5

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Apr 16, 2019 at 08:38:33PM +0200, Christian König wrote:
> Each importer can now provide an invalidate_mappings callback.
> 
> This allows the exporter to provide the mappings without the need to pin
> the backing store.
> 
> v2: don't try to invalidate mappings when the callback is NULL,
>     lock the reservation obj while using the attachments,
>     add helper to set the callback
> v3: move flag for invalidation support into the DMA-buf,
>     use new attach_info structure to set the callback
> v4: use importer_priv field instead of mangling exporter priv.
> v5: drop invalidation_supported flag
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
>  drivers/dma-buf/dma-buf.c | 37 +++++++++++++++++++++++++++++++++++++
>  include/linux/dma-buf.h   | 33 +++++++++++++++++++++++++++++++--
>  2 files changed, 68 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 83c92bfd964c..a3738fab3927 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -563,6 +563,8 @@ struct dma_buf_attachment *dma_buf_attach(const struct dma_buf_attach_info *info
>  
>  	attach->dev = info->dev;
>  	attach->dmabuf = dmabuf;
> +	attach->importer_priv = info->importer_priv;
> +	attach->invalidate = info->invalidate;
>  
>  	mutex_lock(&dmabuf->lock);
>  
> @@ -571,7 +573,9 @@ struct dma_buf_attachment *dma_buf_attach(const struct dma_buf_attach_info *info
>  		if (ret)
>  			goto err_attach;
>  	}
> +	reservation_object_lock(dmabuf->resv, NULL);
>  	list_add(&attach->node, &dmabuf->attachments);
> +	reservation_object_unlock(dmabuf->resv);
>  
>  	mutex_unlock(&dmabuf->lock);
>  
> @@ -615,7 +619,9 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>  					   DMA_BIDIRECTIONAL);
>  
>  	mutex_lock(&dmabuf->lock);
> +	reservation_object_lock(dmabuf->resv, NULL);
>  	list_del(&attach->node);
> +	reservation_object_unlock(dmabuf->resv);
>  	if (dmabuf->ops->detach)
>  		dmabuf->ops->detach(dmabuf, attach);
>  
> @@ -653,7 +659,16 @@ dma_buf_map_attachment_locked(struct dma_buf_attachment *attach,
>  	if (attach->sgt)
>  		return attach->sgt;
>  
> +	/*
> +	 * Mapping a DMA-buf can trigger its invalidation, prevent sending this
> +	 * event to the caller by temporary removing this attachment from the
> +	 * list.
> +	 */
> +	if (attach->invalidate)
> +		list_del(&attach->node);
>  	sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> +	if (attach->invalidate)
> +		list_add(&attach->node, &attach->dmabuf->attachments);
>  	if (!sg_table)
>  		sg_table = ERR_PTR(-ENOMEM);
>  
> @@ -751,6 +766,26 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
>  }
>  EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
>  
> +/**
> + * dma_buf_invalidate_mappings - invalidate all mappings of this dma_buf
> + *
> + * @dmabuf:	[in]	buffer which mappings should be invalidated
> + *
> + * Informs all attachmenst that they need to destroy and recreated all their
> + * mappings.
> + */
> +void dma_buf_invalidate_mappings(struct dma_buf *dmabuf)
> +{
> +	struct dma_buf_attachment *attach;
> +
> +	reservation_object_assert_held(dmabuf->resv);
> +
> +	list_for_each_entry(attach, &dmabuf->attachments, node)
> +		if (attach->invalidate)
> +			attach->invalidate(attach);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_invalidate_mappings);
> +
>  /**
>   * DOC: cpu access
>   *
> @@ -1163,10 +1198,12 @@ static int dma_buf_debug_show(struct seq_file *s, void *unused)
>  		seq_puts(s, "\tAttached Devices:\n");
>  		attach_count = 0;
>  
> +		reservation_object_lock(buf_obj->resv, NULL);
>  		list_for_each_entry(attach_obj, &buf_obj->attachments, node) {
>  			seq_printf(s, "\t%s\n", dev_name(attach_obj->dev));
>  			attach_count++;
>  		}
> +		reservation_object_unlock(buf_obj->resv);
>  
>  		seq_printf(s, "Total %d devices attached\n\n",
>  				attach_count);
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 7e23758db3a4..ece4638359a8 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -324,6 +324,7 @@ struct dma_buf {
>   * @dev: device attached to the buffer.
>   * @node: list of dma_buf_attachment.
>   * @priv: exporter specific attachment data.
> + * @importer_priv: importer specific attachment data.
>   *
>   * This structure holds the attachment information between the dma_buf buffer
>   * and its user device(s). The list contains one attachment struct per device
> @@ -340,6 +341,29 @@ struct dma_buf_attachment {
>  	struct list_head node;
>  	void *priv;
>  	struct sg_table *sgt;
> +	void *importer_priv;
> +
> +	/**
> +	 * @invalidate:
> +	 *
> +	 * Optional callback provided by the importer of the dma-buf.
> +	 *
> +	 * If provided the exporter can avoid pinning the backing store while
> +	 * mappings exists.
> +	 *
> +	 * The function is called with the lock of the reservation object
> +	 * associated with the dma_buf held and the mapping function must be
> +	 * called with this lock held as well. This makes sure that no mapping
> +	 * is created concurrently with an ongoing invalidation.
> +	 *
> +	 * After the callback all existing mappings are still valid until all
> +	 * fences in the dma_bufs reservation object are signaled, but should be
> +	 * destroyed by the importer as soon as possible.
> +	 *
> +	 * New mappings can be created immediately, but can't be used before the
> +	 * exclusive fence in the dma_bufs reservation object is signaled.
> +	 */
> +	void (*invalidate)(struct dma_buf_attachment *attach);

I would put the long kerneldoc into dma_buf_attach_info (as an inline
comment, you can mix the styles). And reference it from here with
something like

"Set from &dma_buf_attach_info.invalidate in dma_buf_attach(), see there
for more information."

This here feels a bit too much hidden.
-Daniel

>  };
>  
>  /**
> @@ -378,8 +402,10 @@ struct dma_buf_export_info {
>  
>  /**
>   * struct dma_buf_attach_info - holds information needed to attach to a dma_buf
> - * @dmabuf:	the exported dma_buf
> - * @dev:	the device which wants to import the attachment
> + * @dmabuf:		the exported dma_buf
> + * @dev:		the device which wants to import the attachment
> + * @importer_priv:	private data of importer to this attachment
> + * @invalidate:		callback to use for invalidating mappings
>   *
>   * This structure holds the information required to attach to a buffer. Used
>   * with dma_buf_attach() only.
> @@ -387,6 +413,8 @@ struct dma_buf_export_info {
>  struct dma_buf_attach_info {
>  	struct dma_buf *dmabuf;
>  	struct device *dev;
> +	void *importer_priv;
> +	void (*invalidate)(struct dma_buf_attachment *attach);
>  };
>  
>  /**
> @@ -423,6 +451,7 @@ void dma_buf_unmap_attachment_locked(struct dma_buf_attachment *,
>  				     enum dma_data_direction);
>  void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
>  				enum dma_data_direction);
> +void dma_buf_invalidate_mappings(struct dma_buf *dma_buf);
>  int dma_buf_begin_cpu_access(struct dma_buf *dma_buf,
>  			     enum dma_data_direction dir);
>  int dma_buf_end_cpu_access(struct dma_buf *dma_buf,
> -- 
> 2.17.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch