Re: [Intel-gfx] [PATCH 1/6] dma-buf: add dynamic DMA-buf handling v10

Daniel Vetter
2019-06-21T09:20:22Z

On Tue, Jun 18, 2019 at 01:54:50PM +0200, Christian König wrote:
> On the exporter side we add optional explicit pinning callbacks. If those
> callbacks are implemented the framework no longer caches sg tables and the
> map/unmap callbacks are always called with the lock of the reservation object
> held.
>
> On the importer side we add an optional invalidate callback. This callback is
> used by the exporter to inform the importers that their mappings should be
> destroyed as soon as possible.
>
> 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
> v6: squash together with pin/unpin changes
> v7: pin/unpin takes an attachment now
> v8: nuke dma_buf_attachment_(map|unmap)_locked,
> everything is now handled backward compatible
> v9: always cache when export/importer don't agree on dynamic handling
> v10: minimal style cleanup
>
> Signed-off-by: Christian König <christian.koenig@amd.com>
> ---
> drivers/dma-buf/dma-buf.c | 188 ++++++++++++++++++++++++++++++++++++--
> include/linux/dma-buf.h | 109 ++++++++++++++++++++--
> 2 files changed, 283 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 6c15deb5d4ad..9c9c95a88655 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -531,6 +531,9 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
> return ERR_PTR(-EINVAL);
> }
>
> + if (WARN_ON(exp_info->ops->cache_sgt_mapping && exp_info->ops->pin))
> + return ERR_PTR(-EINVAL);
> +
> if (!try_module_get(exp_info->owner))
> return ERR_PTR(-ENOENT);
>
> @@ -651,10 +654,12 @@ void dma_buf_put(struct dma_buf *dmabuf)
> EXPORT_SYMBOL_GPL(dma_buf_put);
>
> /**
> - * dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
> + * dma_buf_dynamic_attach - Add the device to dma_buf's attachments list; optionally,
> * calls attach() of dma_buf_ops to allow device-specific attach functionality
> - * @dmabuf: [in] buffer to attach device to.
> - * @dev: [in] device to be attached.
> + * @dmabuf: [in] buffer to attach device to.
> + * @dev: [in] device to be attached.
> + * @importer_ops [in] importer operations for the attachment
> + * @importer_priv [in] importer private pointer for the attachment
> *
> * Returns struct dma_buf_attachment pointer for this attachment. Attachments
> * must be cleaned up by calling dma_buf_detach().
> @@ -668,8 +673,10 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
> * accessible to @dev, and cannot be moved to a more suitable place. This is
> * indicated with the error code -EBUSY.
> */
> -struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> - struct device *dev)
> +struct dma_buf_attachment *
> +dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> + const struct dma_buf_attach_ops *importer_ops,
> + void *importer_priv)
> {
> struct dma_buf_attachment *attach;
> int ret;
> @@ -683,6 +690,8 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
>
> attach->dev = dev;
> attach->dmabuf = dmabuf;
> + attach->importer_ops = importer_ops;
> + attach->importer_priv = importer_priv;
>
> mutex_lock(&dmabuf->lock);
>
> @@ -691,16 +700,72 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> 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);
>
> + /* When either the importer or the exporter can't handle dynamic
> + * mappings we cache the mapping here to avoid issues with the
> + * reservation object lock.
> + */
> + if (dma_buf_attachment_is_dynamic(attach) !=
> + dma_buf_is_dynamic(dmabuf)) {
> + struct sg_table *sgt;
> +
> + if (dma_buf_is_dynamic(attach->dmabuf)) {
> + reservation_object_lock(attach->dmabuf->resv, NULL);
> + ret = dma_buf_pin(attach);
> + if (ret)
> + goto err_unlock;
> + }
> +
> + sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
> + if (!sgt)
> + sgt = ERR_PTR(-ENOMEM);
> + if (IS_ERR(sgt)) {
> + ret = PTR_ERR(sgt);
> + goto err_unpin;
> + }
> + if (dma_buf_is_dynamic(attach->dmabuf))
> + reservation_object_unlock(attach->dmabuf->resv);
> + attach->sgt = sgt;
> + attach->dir = DMA_BIDIRECTIONAL;
> + }
> +
> return attach;
>
> err_attach:
> kfree(attach);
> mutex_unlock(&dmabuf->lock);
> return ERR_PTR(ret);
> +
> +err_unpin:
> + if (dma_buf_is_dynamic(attach->dmabuf))
> + dma_buf_unpin(attach);
> +
> +err_unlock:
> + if (dma_buf_is_dynamic(attach->dmabuf))
> + reservation_object_unlock(attach->dmabuf->resv);
> +
> + dma_buf_detach(dmabuf, attach);
> + return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_dynamic_attach);
> +
> +/**
> + * dma_buf_attach - Wrapper for dma_buf_dynamic_attach
> + * @dmabuf: [in] buffer to attach device to.
> + * @dev: [in] device to be attached.
> + *
> + * Wrapper to call dma_buf_dynamic_attach() for drivers which still use a static
> + * mapping.
> + */
> +struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> + struct device *dev)
> +{
> + return dma_buf_dynamic_attach(dmabuf, dev, NULL, NULL);
> }
> EXPORT_SYMBOL_GPL(dma_buf_attach);
>
> @@ -717,11 +782,22 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
> if (WARN_ON(!dmabuf || !attach))
> return;
>
> - if (attach->sgt)
> + if (attach->sgt) {
> + if (dma_buf_is_dynamic(attach->dmabuf))
> + reservation_object_lock(attach->dmabuf->resv, NULL);
> +
> dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
>
> + if (dma_buf_is_dynamic(attach->dmabuf)) {
> + dma_buf_unpin(attach);
> + reservation_object_unlock(attach->dmabuf->resv);
> + }
> + }
> +
> 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);
>
> @@ -730,6 +806,44 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
> }
> EXPORT_SYMBOL_GPL(dma_buf_detach);
>
> +/**
> + * dma_buf_pin - Lock down the DMA-buf
> + *
> + * @attach: [in] attachment which should be pinned
> + *
> + * Returns:
> + * 0 on success, negative error code on failure.
> + */
> +int dma_buf_pin(struct dma_buf_attachment *attach)
> +{
> + struct dma_buf *dmabuf = attach->dmabuf;
> + int ret = 0;
> +
> + reservation_object_assert_held(dmabuf->resv);
> +
> + if (dmabuf->ops->pin)
> + ret = dmabuf->ops->pin(attach);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_pin);
> +
> +/**
> + * dma_buf_unpin - Remove lock from DMA-buf
> + *
> + * @attach: [in] attachment which should be unpinned
> + */
> +void dma_buf_unpin(struct dma_buf_attachment *attach)
> +{
> + struct dma_buf *dmabuf = attach->dmabuf;
> +
> + reservation_object_assert_held(dmabuf->resv);
> +
> + if (dmabuf->ops->unpin)
> + dmabuf->ops->unpin(attach);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_unpin);
> +
> /**
> * dma_buf_map_attachment - Returns the scatterlist table of the attachment;
> * mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
> @@ -749,6 +863,7 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> enum dma_data_direction direction)
> {
> struct sg_table *sg_table;
> + int r;
>
> might_sleep();
>
> @@ -767,10 +882,38 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> return attach->sgt;
> }
>
> + if (dma_buf_attachment_is_dynamic(attach)) {
> + reservation_object_assert_held(attach->dmabuf->resv);
> +
> + /*
> + * Mapping a DMA-buf can trigger its invalidation, prevent
> + * sending this event to the caller by temporary removing
> + * this attachment from the list.
> + */
> + list_del(&attach->node);

I'm still hung up about this, that still feels like leaking random ttm
implementation details into the dma-buf interfaces. And it's asymmetric:

- When acquiring a buffer mapping (whether p2p or system memory sg or
whatever) we always have to wait for pending fences before we can access
the buffer. At least for full dynamic dma-buf access.

- Same is true when dropping a mapping: We could drop the mapping
immediately, but only actually release it when that fence has signalled.
Then this hack here wouldn't be necessary.

It feels a bit like this is just an artifact of how ttm currently does bo
moves with the shadow bo. There's other ways to fix that, you could just
have a memory manager reservation of a given range or whatever and a
release fence from when it's actually good to use.

Imo the below semantics would be much cleaner:

- invalidate may add new fences
- invalidate _must_ unmap its mappings
- an unmap must wait for current fences before the mapping can be
released.

Imo there's no reason why unmap is special, and the only thing where we
don't use fences to gate access to resources/memory when it's in the
process of getting moved around.

btw this is like the 2nd or 3rd time I'm typing this, haven't seen your
thoughts on this yet.

Thanks, Daniel

> +
> + } else if (dma_buf_is_dynamic(attach->dmabuf)) {
> + reservation_object_lock(attach->dmabuf->resv, NULL);
> + r = dma_buf_pin(attach);
> + if (r) {
> + reservation_object_unlock(attach->dmabuf->resv);
> + return ERR_PTR(r);
> + }
> + }
> +
> sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> if (!sg_table)
> sg_table = ERR_PTR(-ENOMEM);
>
> + if (dma_buf_attachment_is_dynamic(attach)) {
> + list_add(&attach->node, &attach->dmabuf->attachments);
> +
> + } else if (dma_buf_is_dynamic(attach->dmabuf)) {
> + if (IS_ERR(sg_table))
> + dma_buf_unpin(attach);
> + reservation_object_unlock(attach->dmabuf->resv);
> + }
> +
> if (!IS_ERR(sg_table) && attach->dmabuf->ops->cache_sgt_mapping) {
> attach->sgt = sg_table;
> attach->dir = direction;
> @@ -802,10 +945,41 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> if (attach->sgt == sg_table)
> return;
>
> + if (dma_buf_attachment_is_dynamic(attach))
> + reservation_object_assert_held(attach->dmabuf->resv);
> + else if (dma_buf_is_dynamic(attach->dmabuf))
> + reservation_object_lock(attach->dmabuf->resv, NULL);
> +
> attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
> +
> + if (dma_buf_is_dynamic(attach->dmabuf) &&
> + !dma_buf_attachment_is_dynamic(attach)) {
> + dma_buf_unpin(attach);
> + reservation_object_unlock(attach->dmabuf->resv);
> + }
> }
> 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->importer_ops && attach->importer_ops->invalidate)
> + attach->importer_ops->invalidate(attach);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_invalidate_mappings);
> +
> /**
> * DOC: cpu access
> *
> @@ -1225,10 +1399,12 @@ 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 01ad5b942a6f..f9c96bf56bc8 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -92,14 +92,40 @@ struct dma_buf_ops {
> */
> void (*detach)(struct dma_buf *, struct dma_buf_attachment *);
>
> + /**
> + * @pin:
> + *
> + * This is called by dma_buf_pin and lets the exporter know that the
> + * DMA-buf can't be moved any more.
> + *
> + * This is called with the dmabuf->resv object locked.
> + *
> + * This callback is optional.
> + *
> + * Returns:
> + *
> + * 0 on success, negative error code on failure.
> + */
> + int (*pin)(struct dma_buf_attachment *attach);
> +
> + /**
> + * @unpin:
> + *
> + * This is called by dma_buf_unpin and lets the exporter know that the
> + * DMA-buf can be moved again.
> + *
> + * This is called with the dmabuf->resv object locked.
> + *
> + * This callback is optional.
> + */
> + void (*unpin)(struct dma_buf_attachment *attach);
> +
> /**
> * @map_dma_buf:
> *
> * This is called by dma_buf_map_attachment() and is used to map a
> * shared &dma_buf into device address space, and it is mandatory. It
> - * can only be called if @attach has been called successfully. This
> - * essentially pins the DMA buffer into place, and it cannot be moved
> - * any more
> + * can only be called if @attach has been called successfully.
> *
> * This call may sleep, e.g. when the backing storage first needs to be
> * allocated, or moved to a location suitable for all currently attached
> @@ -120,6 +146,9 @@ struct dma_buf_ops {
> * any other kind of sharing that the exporter might wish to make
> * available to buffer-users.
> *
> + * This is always called with the dmabuf->resv object locked when
> + * the pin/unpin callbacks are implemented.
> + *
> * Returns:
> *
> * A &sg_table scatter list of or the backing storage of the DMA buffer,
> @@ -137,9 +166,6 @@ struct dma_buf_ops {
> *
> * This is called by dma_buf_unmap_attachment() and should unmap and
> * release the &sg_table allocated in @map_dma_buf, and it is mandatory.
> - * It should also unpin the backing storage if this is the last mapping
> - * of the DMA buffer, it the exporter supports backing storage
> - * migration.
> */
> void (*unmap_dma_buf)(struct dma_buf_attachment *,
> struct sg_table *,
> @@ -330,6 +356,35 @@ struct dma_buf {
> } cb_excl, cb_shared;
> };
>
> +/**
> + * struct dma_buf_attach_ops - importer operations for an attachment
> + * @invalidate: [optional] invalidate all mappings made using this attachment.
> + *
> + * Attachment operations implemented by the importer.
> + */
> +struct dma_buf_attach_ops {
> + /**
> + * @invalidate:
> + *
> + * If the invalidate callback is provided the framework can avoid
> + * pinning the backing store while mappings exists.
> + *
> + * This callback 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. After getting an
> + * invalidation callback all mappings should be destroyed by the importer using
> + * the normal dma_buf_unmap_attachment() function 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);
> +};
> +
> /**
> * struct dma_buf_attachment - holds device-buffer attachment data
> * @dmabuf: buffer for this attachment.
> @@ -338,6 +393,8 @@ struct dma_buf {
> * @sgt: cached mapping.
> * @dir: direction of cached mapping.
> * @priv: exporter specific attachment data.
> + * @importer_ops: importer operations for this attachment.
> + * @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
> @@ -355,6 +412,9 @@ struct dma_buf_attachment {
> struct sg_table *sgt;
> enum dma_data_direction dir;
> void *priv;
> +
> + const struct dma_buf_attach_ops *importer_ops;
> + void *importer_priv;
> };
>
> /**
> @@ -405,10 +465,42 @@ static inline void get_dma_buf(struct dma_buf *dmabuf)
> get_file(dmabuf->file);
> }
>
> +/**
> + * dma_buf_is_dynamic - check if a DMA-buf uses dynamic mappings.
> + * @dmabuf: the DMA-buf to check
> + *
> + * Returns true if a DMA-buf exporter wants to create dynamic sg table mappings
> + * for each attachment. False if only a single static sg table should be used.
> + */
> +static inline bool dma_buf_is_dynamic(struct dma_buf *dmabuf)
> +{
> + return !!dmabuf->ops->pin;
> +}
> +
> +/**
> + * dma_buf_attachment_is_dynamic - check if a DMA-buf attachment uses dynamic
> + * mappinsg
> + * @attach: the DMA-buf attachment to check
> + *
> + * Returns true if a DMA-buf importer wants to use dynamic sg table mappings and
> + * calls the map/unmap functions with the reservation object locked.
> + */
> +static inline bool
> +dma_buf_attachment_is_dynamic(struct dma_buf_attachment *attach)
> +{
> + return attach->importer_ops && attach->importer_ops->invalidate;
> +}
> +
> struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> - struct device *dev);
> + struct device *dev);
> +struct dma_buf_attachment *
> +dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> + const struct dma_buf_attach_ops *importer_ops,
> + void *importer_priv);
> void dma_buf_detach(struct dma_buf *dmabuf,
> - struct dma_buf_attachment *dmabuf_attach);
> + struct dma_buf_attachment *attach);
> +int dma_buf_pin(struct dma_buf_attachment *attach);
> +void dma_buf_unpin(struct dma_buf_attachment *attach);
>
> struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info);
>
> @@ -420,6 +512,7 @@ struct sg_table *dma_buf_map_attachment(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
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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