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Reply-To: christian.koenig@amd.com
Subject: Re: [PATCH 04/12] dma-buf: add optional invalidate_mappings callback
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References: <20190416183841.1577-1-christian.koenig@amd.com>
 <20190416183841.1577-5-christian.koenig@amd.com>
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From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <ckoenig.leichtzumerken@gmail.com>
Message-ID: <03a04d1d-9bc0-8f20-0436-b0f0017f0506@gmail.com>
Date:   Wed, 17 Apr 2019 21:13:22 +0200
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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@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);
> 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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