On Wed, May 15, 2019 at 04:38:26PM +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
>
> Signed-off-by: Christian König <christian.koe...@amd.com>
Sorry for taking so long, I'm kinda starting to dread this series a bit so
engaged into some good old fashioned procrastinating :-/
> ---
> drivers/dma-buf/dma-buf.c | 157 ++++++++++++++++++++++++++++++++++++--
> include/linux/dma-buf.h | 109 ++++++++++++++++++++++++--
> 2 files changed, 253 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index a2d34c6b80a5..85026d9e978d 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -409,6 +409,9 @@ 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);
>
> @@ -530,10 +533,12 @@ 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().
> @@ -547,8 +552,10 @@ 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;
> @@ -562,6 +569,8 @@ 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);
>
> @@ -570,10 +579,31 @@ 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);
>
Just this functional comment, since I think api detail polishing is
premature if we're not yet aware of how this works.
> + /* When the importer is dynamic but the exporter isn't we need to cache
> + * the mapping or otherwise would run into issues with the reservation
> + * object lock.
> + */
> + if (dma_buf_attachment_is_dynamic(attach) &&
> + !dma_buf_is_dynamic(dmabuf)) {
Isn't this the wrong way round? dynamic importers should be perfectly fine
with the reservation locks in their map/unmap paths, it's importers
calling exporters there.
The real problem is a not-dynamic importer, which hasn't be adjusted to
allow the reservation lock in their paths where they map/unmap a buffer,
with a dynamic exporter. That's where we need to cache the mapping to
avoid the deadlock (or having to change everyone)
> + struct sg_table *sgt;
> +
> + sgt = dmabuf->ops->map_dma_buf(attach, DMA_BIDIRECTIONAL);
And unfortunately the non-dynamic, i.e. legacy/current code importer is
also the one which uses other flags than DMA_BIDIRECTIONAL. At least on
ARM, and that's the only place where this matters because there the dma
api might do cache flushing.
Cheers, Daniel
> + if (!sgt)
> + sgt = ERR_PTR(-ENOMEM);
> + if (IS_ERR(sgt)) {
> + dma_buf_detach(dmabuf, attach);
> + return ERR_CAST(sgt);
> + }
> + attach->sgt = sgt;
> + attach->dir = DMA_BIDIRECTIONAL;
> + }
> +
> return attach;
>
> err_attach:
> @@ -581,6 +611,21 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf
> *dmabuf,
> mutex_unlock(&dmabuf->lock);
> 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);
>
> /**
> @@ -600,7 +645,9 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct
> dma_buf_attachment *attach)
> dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
>
> 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);
>
> @@ -609,6 +656,44 @@ 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
> @@ -628,6 +713,7 @@ 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();
>
> @@ -646,10 +732,38 @@ 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);
> +
> + } 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;
> @@ -681,10 +795,41 @@ 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
> *
> @@ -1097,10 +1242,12 @@ 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 45b9767e67ec..5309f1ceaefe 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -99,14 +99,40 @@ 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 *);
> +
> + /**
> + * @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 *);
> +
> /**
> * @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
> @@ -127,6 +153,9 @@ 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,
> @@ -144,9 +173,6 @@ 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 *,
> @@ -311,6 +337,35 @@ 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.
> @@ -319,6 +374,8 @@ 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
> @@ -336,6 +393,9 @@ 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;
> };
>
> /**
> @@ -386,10 +446,42 @@ 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);
>
> @@ -401,6 +493,7 @@ 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
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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