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

[Christian König <ckoenig.leichtzumerken@xxxxxxxxx>]

Am 17.04.19 um 21:07 schrieb Daniel Vetter:
> 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@xxxxxxx>
> > ---
> >   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);
> Just noticed this: Why do we need this? invalidate needs the reservation
> lock, as does map_attachment. It should be impssoble to have someone else
> sneak in here.

I was having problems with self triggered invalidations.

E.g. client A tries to map an attachment, that in turn causes the buffer 
to move to a new place and client A is informed about that movement with 
an invalidation.

Christian.

> -Daniel
>
> >   	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);
> >   };
> >   
> >   /**
> > @@ -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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