Re: [Intel-gfx] [PATCH 1/5] dma-buf: add dynamic DMA-buf handling v14

Daniel Vetter
2019-11-05T10:20:54Z

On Tue, Oct 29, 2019 at 11:40:45AM +0100, Christian König wrote:
> On the exporter side we add optional explicit pinning callbacks. Which are
> called when the importer doesn't implement dynamic handling, move notification
> or need the DMA-buf locked in place for its use case.
>
> On the importer side we add an optional move_notify 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
> v11: drop automatically re-entry avoidance
> v12: rename callback to move_notify
> v13: add might_lock in appropriate places
> v14: rebase on separated locking change
>
> Signed-off-by: Christian König <christian.koenig@amd.com>

Bunch of nitpicks/safety check comments here, I'll post the big question
stuff on the cover letter.

> ---
> drivers/dma-buf/dma-buf.c | 106 ++++++++++++++++++--
> drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c | 6 +-
> include/linux/dma-buf.h | 78 ++++++++++++--
> 3 files changed, 170 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index d377b4ca66bf..ce293cee76ed 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -529,6 +529,10 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
> exp_info->ops->dynamic_mapping))
> return ERR_PTR(-EINVAL);
>
> + if (WARN_ON(!exp_info->ops->dynamic_mapping &&
> + (exp_info->ops->pin || exp_info->ops->unpin)))
> + return ERR_PTR(-EINVAL);

Imo make this stronger, have a dynamic mapping iff there's both a pin and
unpin function. Otherwise this doesn't make a lot of sense to me.

> +
> if (!try_module_get(exp_info->owner))
> return ERR_PTR(-ENOENT);
>
> @@ -653,7 +657,8 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
> * 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.
> - * @dynamic_mapping: [in] calling convention for map/unmap
> + * @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().
> @@ -669,7 +674,8 @@ EXPORT_SYMBOL_GPL(dma_buf_put);
> */
> struct dma_buf_attachment *
> dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> - bool dynamic_mapping)
> + const struct dma_buf_attach_ops *importer_ops,
> + void *importer_priv)
> {
> struct dma_buf_attachment *attach;
> int ret;
> @@ -683,7 +689,8 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>
> attach->dev = dev;
> attach->dmabuf = dmabuf;
> - attach->dynamic_mapping = dynamic_mapping;
> + attach->importer_ops = importer_ops;
> + attach->importer_priv = importer_priv;
>
> if (dmabuf->ops->attach) {
> ret = dmabuf->ops->attach(dmabuf, attach);
> @@ -702,15 +709,19 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> dma_buf_is_dynamic(dmabuf)) {
> struct sg_table *sgt;
>
> - if (dma_buf_is_dynamic(attach->dmabuf))
> + if (dma_buf_is_dynamic(attach->dmabuf)) {
> dma_resv_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_unlock;
> + goto err_unpin;
> }
> if (dma_buf_is_dynamic(attach->dmabuf))
> dma_resv_unlock(attach->dmabuf->resv);
> @@ -724,6 +735,10 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
> kfree(attach);
> 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))
> dma_resv_unlock(attach->dmabuf->resv);
> @@ -744,7 +759,7 @@ EXPORT_SYMBOL_GPL(dma_buf_dynamic_attach);
> struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> struct device *dev)
> {
> - return dma_buf_dynamic_attach(dmabuf, dev, false);
> + return dma_buf_dynamic_attach(dmabuf, dev, NULL, NULL);
> }
> EXPORT_SYMBOL_GPL(dma_buf_attach);
>
> @@ -767,8 +782,10 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>
> dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
>
> - if (dma_buf_is_dynamic(attach->dmabuf))
> + if (dma_buf_is_dynamic(attach->dmabuf)) {
> + dma_buf_unpin(attach);
> dma_resv_unlock(attach->dmabuf->resv);
> + }
> }
>
> dma_resv_lock(dmabuf->resv, NULL);
> @@ -781,6 +798,44 @@ 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;
> +
> + dma_resv_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;
> +
> + dma_resv_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
> @@ -800,6 +855,7 @@ 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();
>
> @@ -821,13 +877,23 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
> return attach->sgt;
> }
>
> - if (dma_buf_is_dynamic(attach->dmabuf))
> + if (dma_buf_is_dynamic(attach->dmabuf)) {
> dma_resv_assert_held(attach->dmabuf->resv);
> + if (!attach->importer_ops->move_notify) {

Imo just require ->move_notify for importers that give you an ops
function. Doesn't really make sense to allow dynamic without support
->move_notify.

> + r = dma_buf_pin(attach);
> + if (r)
> + return ERR_PTR(r);
> + }
> + }
>
> sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
> if (!sg_table)
> sg_table = ERR_PTR(-ENOMEM);
>
> + if (IS_ERR(sg_table) && dma_buf_is_dynamic(attach->dmabuf) &&
> + !attach->importer_ops->move_notify)
> + dma_buf_unpin(attach);
> +
> if (!IS_ERR(sg_table) && attach->dmabuf->ops->cache_sgt_mapping) {
> attach->sgt = sg_table;
> attach->dir = direction;
> @@ -866,9 +932,33 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
> dma_resv_assert_held(attach->dmabuf->resv);
>
> attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
> +
> + if (dma_buf_is_dynamic(attach->dmabuf) &&
> + !attach->importer_ops->move_notify)
> + dma_buf_unpin(attach);
> }
> EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
>
> +/**
> + * dma_buf_move_notify - notify attachments that DMA-buf is moving
> + *
> + * @dmabuf: [in] buffer which is moving
> + *
> + * Informs all attachmenst that they need to destroy and recreated all their
> + * mappings.
> + */
> +void dma_buf_move_notify(struct dma_buf *dmabuf)
> +{
> + struct dma_buf_attachment *attach;
> +
> + dma_resv_assert_held(dmabuf->resv);
> +
> + list_for_each_entry(attach, &dmabuf->attachments, node)
> + if (attach->importer_ops && attach->importer_ops->move_notify)
> + attach->importer_ops->move_notify(attach);
> +}
> +EXPORT_SYMBOL_GPL(dma_buf_move_notify);
> +
> /**
> * DOC: cpu access
> *
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> index d5bcdfefbad6..8e5a68107556 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
> @@ -415,6 +415,9 @@ amdgpu_dma_buf_create_obj(struct drm_device *dev, struct dma_buf *dma_buf)
> return ERR_PTR(ret);
> }
>
> +static const struct dma_buf_attach_ops amdgpu_dma_buf_attach_ops = {
> +};
> +
> /**
> * amdgpu_gem_prime_import - &drm_driver.gem_prime_import implementation
> * @dev: DRM device
> @@ -447,7 +450,8 @@ struct drm_gem_object *amdgpu_gem_prime_import(struct drm_device *dev,
> if (IS_ERR(obj))
> return obj;
>
> - attach = dma_buf_dynamic_attach(dma_buf, dev->dev, true);
> + attach = dma_buf_dynamic_attach(dma_buf, dev->dev,
> + &amdgpu_dma_buf_attach_ops, NULL);
> if (IS_ERR(attach)) {
> drm_gem_object_put(obj);
> return ERR_CAST(attach);
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index af73f835c51c..7456bb937635 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -93,14 +93,40 @@ 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.

I think we should add a warning here that pinning is only ok for limited
use-cases (like scanout or similar), and not as part of general buffer
management.

i915 uses temporary pins through it's execbuf management (and everywhere
else), so we have a _lot_ of people in dri-devel with quite different
ideas of what this might be for :-)

> + *
> + * 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
> @@ -141,9 +167,6 @@ 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.

This is still valid for non-dynamic exporters. Imo keep but clarify that.

> */
> void (*unmap_dma_buf)(struct dma_buf_attachment *,
> struct sg_table *,
> @@ -336,6 +359,34 @@ struct dma_buf {
> } cb_excl, cb_shared;
> };
>
> +/**
> + * struct dma_buf_attach_ops - importer operations for an attachment
> + * @move_notify: [optional] notification that the DMA-buf is moving
> + *
> + * Attachment operations implemented by the importer.
> + */
> +struct dma_buf_attach_ops {
> + /**
> + * @move_notify
> + *
> + * If this 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 move operation.
> + *
> + * Mappings stay valid and are not directly affected by this callback.
> + * But the DMA-buf can now be in a different physical location, so all
> + * mappings should be destroyed and re-created as soon as possible.
> + *
> + * New mappings can be created after this callback returns, and will
> + * point to the new location of the DMA-buf.
> + */
> + void (*move_notify)(struct dma_buf_attachment *attach);
> +};
> +
> /**
> * struct dma_buf_attachment - holds device-buffer attachment data
> * @dmabuf: buffer for this attachment.
> @@ -344,8 +395,9 @@ struct dma_buf {
> * @sgt: cached mapping.
> * @dir: direction of cached mapping.
> * @priv: exporter specific attachment data.
> - * @dynamic_mapping: true if dma_buf_map/unmap_attachment() is called with the
> - * dma_resv lock held.
> + * @importer_ops: importer operations for this attachment, if provided
> + * dma_buf_map/unmap_attachment() must be called with the dma_resv lock held.
> + * @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
> @@ -362,7 +414,8 @@ struct dma_buf_attachment {
> struct list_head node;
> struct sg_table *sgt;
> enum dma_data_direction dir;
> - bool dynamic_mapping;
> + const struct dma_buf_attach_ops *importer_ops;
> + void *importer_priv;
> void *priv;
> };
>
> @@ -438,16 +491,19 @@ static inline bool dma_buf_is_dynamic(struct dma_buf *dmabuf)
> static inline bool
> dma_buf_attachment_is_dynamic(struct dma_buf_attachment *attach)
> {
> - return attach->dynamic_mapping;
> + return !!attach->importer_ops;

Hm why not do the same for exporters, and make them dynamic iff they have
pin/unpin?
-Daniel

> }
>
> 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,
> - bool dynamic_mapping);
> + const struct dma_buf_attach_ops *importer_ops,
> + void *importer_priv);
> void dma_buf_detach(struct dma_buf *dmabuf,
> 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);
>
> --
> 2.17.1
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

--
Daniel Vetter
Software Engineer, Intel Corporation