Message-ID: <bd5adb0e-af98-528f-d6f9-9d5888ff2412@oracle.com>
Date:   Tue, 12 Jun 2018 22:58:30 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Oleksandr Andrushchenko <andr2000@...il.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
        jgross@...e.com, konrad.wilk@...cle.com
Cc:     daniel.vetter@...el.com, dongwon.kim@...el.com,
        matthew.d.roper@...el.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: Re: [PATCH v3 8/9] xen/gntdev: Implement dma-buf export functionality



On 06/12/2018 09:41 AM, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
> 
> 1. Create a dma-buf from grant references provided by the foreign
>     domain. By default dma-buf is backed by system memory pages, but
>     by providing GNTDEV_DMA_FLAG_XXX flags it can also be created
>     as a DMA write-combine/coherent buffer, e.g. allocated with
>     corresponding dma_alloc_xxx API.
>     Export the resulting buffer as a new dma-buf.
> 
> 2. Implement waiting for the dma-buf to be released: block until the
>     dma-buf with the file descriptor provided is released.
>     If within the time-out provided the buffer is not released then
>     -ETIMEDOUT error is returned. If the buffer with the file descriptor
>     does not exist or has already been released, then -ENOENT is
>     returned. For valid file descriptors this must not be treated as
>     error.
> 
> 3. Make gntdev's common code and structures available to dma-buf.
> 
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
> ---
>   drivers/xen/gntdev-common.h |   4 +
>   drivers/xen/gntdev-dmabuf.c | 470 +++++++++++++++++++++++++++++++++++-
>   drivers/xen/gntdev.c        |  10 +
>   3 files changed, 482 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/xen/gntdev-common.h b/drivers/xen/gntdev-common.h
> index a3408fd39b07..72f80dbce861 100644
> --- a/drivers/xen/gntdev-common.h
> +++ b/drivers/xen/gntdev-common.h
> @@ -89,4 +89,8 @@ bool gntdev_account_mapped_pages(int count);
>   
>   int gntdev_map_grant_pages(struct gntdev_grant_map *map);
>   
> +#ifdef CONFIG_XEN_GNTDEV_DMABUF
> +void gntdev_remove_map(struct gntdev_priv *priv, struct gntdev_grant_map *map);
> +#endif
> +
>   #endif
> diff --git a/drivers/xen/gntdev-dmabuf.c b/drivers/xen/gntdev-dmabuf.c
> index dc57c6a25525..84cba67c6ad7 100644
> --- a/drivers/xen/gntdev-dmabuf.c
> +++ b/drivers/xen/gntdev-dmabuf.c
> @@ -3,13 +3,53 @@
>   /*
>    * Xen dma-buf functionality for gntdev.
>    *
> + * DMA buffer implementation is based on drivers/gpu/drm/drm_prime.c.
> + *
>    * Copyright (c) 2018 Oleksandr Andrushchenko, EPAM Systems Inc.
>    */
>   
> +#include <linux/dma-buf.h>
>   #include <linux/slab.h>
>   
> +#include <xen/grant_table.h>
> +#include <xen/gntdev.h>
> +
> +#include "gntdev-common.h"
>   #include "gntdev-dmabuf.h"
>   
> +struct gntdev_dmabuf {
> +	struct gntdev_dmabuf_priv *priv;
> +	struct dma_buf *dmabuf;
> +	struct list_head next;
> +	int fd;
> +
> +	union {
> +		struct {
> +			/* Exported buffers are reference counted. */
> +			struct kref refcount;
> +
> +			struct gntdev_priv *priv;
> +			struct gntdev_grant_map *map;
> +		} exp;
> +	} u;
> +
> +	/* Number of pages this buffer has. */
> +	int nr_pages;
> +	/* Pages of this buffer. */
> +	struct page **pages;
> +};
> +
> +struct gntdev_dmabuf_wait_obj {
> +	struct list_head next;
> +	struct gntdev_dmabuf *gntdev_dmabuf;
> +	struct completion completion;
> +};
> +
> +struct gntdev_dmabuf_attachment {
> +	struct sg_table *sgt;
> +	enum dma_data_direction dir;
> +};
> +
>   struct gntdev_dmabuf_priv {
>   	/* List of exported DMA buffers. */
>   	struct list_head exp_list;
> @@ -23,17 +63,439 @@ struct gntdev_dmabuf_priv {
>   
>   /* Implementation of wait for exported DMA buffer to be released. */
>   
> +static void dmabuf_exp_release(struct kref *kref);
> +
> +static struct gntdev_dmabuf_wait_obj *
> +dmabuf_exp_wait_obj_new(struct gntdev_dmabuf_priv *priv,
> +			struct gntdev_dmabuf *gntdev_dmabuf)
> +{
> +	struct gntdev_dmabuf_wait_obj *obj;
> +
> +	obj = kzalloc(sizeof(*obj), GFP_KERNEL);
> +	if (!obj)
> +		return ERR_PTR(-ENOMEM);
> +
> +	init_completion(&obj->completion);
> +	obj->gntdev_dmabuf = gntdev_dmabuf;
> +
> +	mutex_lock(&priv->lock);
> +	list_add(&obj->next, &priv->exp_wait_list);
> +	/* Put our reference and wait for gntdev_dmabuf's release to fire. */
> +	kref_put(&gntdev_dmabuf->u.exp.refcount, dmabuf_exp_release);
> +	mutex_unlock(&priv->lock);
> +	return obj;
> +}
> +
> +static void dmabuf_exp_wait_obj_free(struct gntdev_dmabuf_priv *priv,
> +				     struct gntdev_dmabuf_wait_obj *obj)
> +{
> +	struct gntdev_dmabuf_wait_obj *cur_obj, *q;
> +
> +	mutex_lock(&priv->lock);
> +	list_for_each_entry_safe(cur_obj, q, &priv->exp_wait_list, next)
> +		if (cur_obj == obj) {
> +			list_del(&obj->next);
> +			kfree(obj);
> +			break;
> +		}
> +	mutex_unlock(&priv->lock);


Do we really need to walk the list?

And if we do, do we need the safe variant of the walk? We are holding 
the lock. Here and elsewhere.


> +}
> +
> +static int dmabuf_exp_wait_obj_wait(struct gntdev_dmabuf_wait_obj *obj,
> +				    u32 wait_to_ms)
> +{
> +	if (wait_for_completion_timeout(&obj->completion,
> +			msecs_to_jiffies(wait_to_ms)) <= 0)
> +		return -ETIMEDOUT;
> +
> +	return 0;
> +}
> +
> +static void dmabuf_exp_wait_obj_signal(struct gntdev_dmabuf_priv *priv,
> +				       struct gntdev_dmabuf *gntdev_dmabuf)
> +{
> +	struct gntdev_dmabuf_wait_obj *obj, *q;
> +
> +	list_for_each_entry_safe(obj, q, &priv->exp_wait_list, next)
> +		if (obj->gntdev_dmabuf == gntdev_dmabuf) {
> +			pr_debug("Found gntdev_dmabuf in the wait list, wake\n");
> +			complete_all(&obj->completion);
> +			break;
> +		}
> +}
> +
> +static struct gntdev_dmabuf *
> +dmabuf_exp_wait_obj_get_by_fd(struct gntdev_dmabuf_priv *priv, int fd)


The name of this routine implies (to me) that we are getting a wait 
object but IIUIC we are getting a gntdev_dmabuf that we are going to 
later associate with a wait object.


> +{
> +	struct gntdev_dmabuf *q, *gntdev_dmabuf, *ret = ERR_PTR(-ENOENT);
> +
> +	mutex_lock(&priv->lock);
> +	list_for_each_entry_safe(gntdev_dmabuf, q, &priv->exp_list, next)
> +		if (gntdev_dmabuf->fd == fd) {
> +			pr_debug("Found gntdev_dmabuf in the wait list\n");
> +			kref_get(&gntdev_dmabuf->u.exp.refcount);
> +			ret = gntdev_dmabuf;
> +			break;
> +		}
> +	mutex_unlock(&priv->lock);
> +	return ret;
> +}
> +
>   int gntdev_dmabuf_exp_wait_released(struct gntdev_dmabuf_priv *priv, int fd,
>   				    int wait_to_ms)
>   {
> -	return -EINVAL;
> +	struct gntdev_dmabuf *gntdev_dmabuf;
> +	struct gntdev_dmabuf_wait_obj *obj;
> +	int ret;
> +
> +	pr_debug("Will wait for dma-buf with fd %d\n", fd);
> +	/*
> +	 * Try to find the DMA buffer: if not found means that
> +	 * either the buffer has already been released or file descriptor
> +	 * provided is wrong.
> +	 */
> +	gntdev_dmabuf = dmabuf_exp_wait_obj_get_by_fd(priv, fd);
> +	if (IS_ERR(gntdev_dmabuf))
> +		return PTR_ERR(gntdev_dmabuf);
> +
> +	/*
> +	 * gntdev_dmabuf still exists and is reference count locked by us now,
> +	 * so prepare to wait: allocate wait object and add it to the wait list,
> +	 * so we can find it on release.
> +	 */
> +	obj = dmabuf_exp_wait_obj_new(priv, gntdev_dmabuf);
> +	if (IS_ERR(obj))
> +		return PTR_ERR(obj);
> +
> +	ret = dmabuf_exp_wait_obj_wait(obj, wait_to_ms);
> +	dmabuf_exp_wait_obj_free(priv, obj);
> +	return ret;
> +}
> +
> +/* DMA buffer export support. */
> +
> +static struct sg_table *
> +dmabuf_pages_to_sgt(struct page **pages, unsigned int nr_pages)
> +{
> +	struct sg_table *sgt;
> +	int ret;
> +
> +	sgt = kmalloc(sizeof(*sgt), GFP_KERNEL);
> +	if (!sgt) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	ret = sg_alloc_table_from_pages(sgt, pages, nr_pages, 0,
> +					nr_pages << PAGE_SHIFT,
> +					GFP_KERNEL);
> +	if (ret)
> +		goto out;
> +
> +	return sgt;
> +
> +out:
> +	kfree(sgt);
> +	return ERR_PTR(ret);
> +}
> +
> +static int dmabuf_exp_ops_attach(struct dma_buf *dma_buf,
> +				 struct device *target_dev,
> +				 struct dma_buf_attachment *attach)
> +{
> +	struct gntdev_dmabuf_attachment *gntdev_dmabuf_attach;
> +
> +	gntdev_dmabuf_attach = kzalloc(sizeof(*gntdev_dmabuf_attach),
> +				       GFP_KERNEL);
> +	if (!gntdev_dmabuf_attach)
> +		return -ENOMEM;
> +
> +	gntdev_dmabuf_attach->dir = DMA_NONE;
> +	attach->priv = gntdev_dmabuf_attach;
> +	return 0;
> +}
> +
> +static void dmabuf_exp_ops_detach(struct dma_buf *dma_buf,
> +				  struct dma_buf_attachment *attach)
> +{
> +	struct gntdev_dmabuf_attachment *gntdev_dmabuf_attach = attach->priv;
> +
> +	if (gntdev_dmabuf_attach) {
> +		struct sg_table *sgt = gntdev_dmabuf_attach->sgt;
> +
> +		if (sgt) {
> +			if (gntdev_dmabuf_attach->dir != DMA_NONE)
> +				dma_unmap_sg_attrs(attach->dev, sgt->sgl,
> +						   sgt->nents,
> +						   gntdev_dmabuf_attach->dir,
> +						   DMA_ATTR_SKIP_CPU_SYNC);
> +			sg_free_table(sgt);
> +		}
> +
> +		kfree(sgt);
> +		kfree(gntdev_dmabuf_attach);
> +		attach->priv = NULL;
> +	}
> +}
> +
> +static struct sg_table *
> +dmabuf_exp_ops_map_dma_buf(struct dma_buf_attachment *attach,
> +			   enum dma_data_direction dir)
> +{
> +	struct gntdev_dmabuf_attachment *gntdev_dmabuf_attach = attach->priv;
> +	struct gntdev_dmabuf *gntdev_dmabuf = attach->dmabuf->priv;
> +	struct sg_table *sgt;
> +
> +	pr_debug("Mapping %d pages for dev %p\n", gntdev_dmabuf->nr_pages,
> +		 attach->dev);
> +
> +	if (dir == DMA_NONE || !gntdev_dmabuf_attach)
> +		return ERR_PTR(-EINVAL);
> +
> +	/* Return the cached mapping when possible. */
> +	if (gntdev_dmabuf_attach->dir == dir)
> +		return gntdev_dmabuf_attach->sgt;
> +
> +	/*
> +	 * Two mappings with different directions for the same attachment are
> +	 * not allowed.
> +	 */
> +	if (gntdev_dmabuf_attach->dir != DMA_NONE)
> +		return ERR_PTR(-EBUSY);
> +
> +	sgt = dmabuf_pages_to_sgt(gntdev_dmabuf->pages,
> +				  gntdev_dmabuf->nr_pages);
> +	if (!IS_ERR(sgt)) {
> +		if (!dma_map_sg_attrs(attach->dev, sgt->sgl, sgt->nents, dir,
> +				      DMA_ATTR_SKIP_CPU_SYNC)) {
> +			sg_free_table(sgt);
> +			kfree(sgt);
> +			sgt = ERR_PTR(-ENOMEM);
> +		} else {
> +			gntdev_dmabuf_attach->sgt = sgt;
> +			gntdev_dmabuf_attach->dir = dir;
> +		}
> +	}
> +	if (IS_ERR(sgt))
> +		pr_debug("Failed to map sg table for dev %p\n", attach->dev);
> +	return sgt;
> +}
> +
> +static void dmabuf_exp_ops_unmap_dma_buf(struct dma_buf_attachment *attach,
> +					 struct sg_table *sgt,
> +					 enum dma_data_direction dir)
> +{
> +	/* Not implemented. The unmap is done at dmabuf_exp_ops_detach(). */
> +}
> +
> +static void dmabuf_exp_release(struct kref *kref)
> +{
> +	struct gntdev_dmabuf *gntdev_dmabuf =
> +		container_of(kref, struct gntdev_dmabuf, u.exp.refcount);
> +
> +	dmabuf_exp_wait_obj_signal(gntdev_dmabuf->priv, gntdev_dmabuf);
> +	list_del(&gntdev_dmabuf->next);
> +	kfree(gntdev_dmabuf);
> +}
> +
> +static void dmabuf_exp_ops_release(struct dma_buf *dma_buf)
> +{
> +	struct gntdev_dmabuf *gntdev_dmabuf = dma_buf->priv;
> +	struct gntdev_dmabuf_priv *priv = gntdev_dmabuf->priv;
> +
> +	gntdev_remove_map(gntdev_dmabuf->u.exp.priv, gntdev_dmabuf->u.exp.map);
> +	mutex_lock(&priv->lock);
> +	kref_put(&gntdev_dmabuf->u.exp.refcount, dmabuf_exp_release);
> +	mutex_unlock(&priv->lock);
> +}
> +
> +static void *dmabuf_exp_ops_kmap_atomic(struct dma_buf *dma_buf,
> +					unsigned long page_num)
> +{
> +	/* Not implemented. */
> +	return NULL;
> +}
> +
> +static void dmabuf_exp_ops_kunmap_atomic(struct dma_buf *dma_buf,
> +					 unsigned long page_num, void *addr)
> +{
> +	/* Not implemented. */
> +}
> +
> +static void *dmabuf_exp_ops_kmap(struct dma_buf *dma_buf,
> +				 unsigned long page_num)
> +{
> +	/* Not implemented. */
> +	return NULL;
> +}
> +
> +static void dmabuf_exp_ops_kunmap(struct dma_buf *dma_buf,
> +				  unsigned long page_num, void *addr)
> +{
> +	/* Not implemented. */
> +}
> +
> +static int dmabuf_exp_ops_mmap(struct dma_buf *dma_buf,
> +			       struct vm_area_struct *vma)
> +{
> +	/* Not implemented. */
> +	return 0;
> +}
> +
> +static const struct dma_buf_ops dmabuf_exp_ops =  {
> +	.attach = dmabuf_exp_ops_attach,
> +	.detach = dmabuf_exp_ops_detach,
> +	.map_dma_buf = dmabuf_exp_ops_map_dma_buf,
> +	.unmap_dma_buf = dmabuf_exp_ops_unmap_dma_buf,
> +	.release = dmabuf_exp_ops_release,
> +	.map = dmabuf_exp_ops_kmap,
> +	.map_atomic = dmabuf_exp_ops_kmap_atomic,
> +	.unmap = dmabuf_exp_ops_kunmap,
> +	.unmap_atomic = dmabuf_exp_ops_kunmap_atomic,
> +	.mmap = dmabuf_exp_ops_mmap,
> +};
> +
> +struct gntdev_dmabuf_export_args {
> +	struct gntdev_priv *priv;
> +	struct gntdev_grant_map *map;
> +	struct gntdev_dmabuf_priv *dmabuf_priv;
> +	struct device *dev;
> +	int count;
> +	struct page **pages;
> +	u32 fd;
> +};
> +
> +static int dmabuf_exp_from_pages(struct gntdev_dmabuf_export_args *args)
> +{
> +	DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> +	struct gntdev_dmabuf *gntdev_dmabuf;
> +	int ret = 0;


Not necessary.

> +
> +	gntdev_dmabuf = kzalloc(sizeof(*gntdev_dmabuf), GFP_KERNEL);
> +	if (!gntdev_dmabuf)
> +		return -ENOMEM;
> +
> +	kref_init(&gntdev_dmabuf->u.exp.refcount);
> +
> +	gntdev_dmabuf->priv = args->dmabuf_priv;
> +	gntdev_dmabuf->nr_pages = args->count;
> +	gntdev_dmabuf->pages = args->pages;
> +	gntdev_dmabuf->u.exp.priv = args->priv;
> +	gntdev_dmabuf->u.exp.map = args->map;
> +
> +	exp_info.exp_name = KBUILD_MODNAME;
> +	if (args->dev->driver && args->dev->driver->owner)
> +		exp_info.owner = args->dev->driver->owner;
> +	else
> +		exp_info.owner = THIS_MODULE;
> +	exp_info.ops = &dmabuf_exp_ops;
> +	exp_info.size = args->count << PAGE_SHIFT;
> +	exp_info.flags = O_RDWR;
> +	exp_info.priv = gntdev_dmabuf;
> +
> +	gntdev_dmabuf->dmabuf = dma_buf_export(&exp_info);
> +	if (IS_ERR(gntdev_dmabuf->dmabuf)) {
> +		ret = PTR_ERR(gntdev_dmabuf->dmabuf);
> +		gntdev_dmabuf->dmabuf = NULL;
> +		goto fail;
> +	}
> +
> +	ret = dma_buf_fd(gntdev_dmabuf->dmabuf, O_CLOEXEC);
> +	if (ret < 0)
> +		goto fail;
> +
> +	gntdev_dmabuf->fd = ret;
> +	args->fd = ret;
> +
> +	pr_debug("Exporting DMA buffer with fd %d\n", ret);
> +
> +	mutex_lock(&args->dmabuf_priv->lock);
> +	list_add(&gntdev_dmabuf->next, &args->dmabuf_priv->exp_list);
> +	mutex_unlock(&args->dmabuf_priv->lock);
> +	return 0;
> +
> +fail:
> +	if (gntdev_dmabuf->dmabuf)
> +		dma_buf_put(gntdev_dmabuf->dmabuf);
> +	kfree(gntdev_dmabuf);
> +	return ret;
> +}
> +
> +static struct gntdev_grant_map *
> +dmabuf_exp_alloc_backing_storage(struct gntdev_priv *priv, int dmabuf_flags,
> +				 int count)
> +{
> +	struct gntdev_grant_map *map;
> +
> +	if (unlikely(count <= 0))
> +		return ERR_PTR(-EINVAL);
> +
> +	if ((dmabuf_flags & GNTDEV_DMA_FLAG_WC) &&
> +	    (dmabuf_flags & GNTDEV_DMA_FLAG_COHERENT)) {
> +		pr_debug("Wrong dma-buf flags: either WC or coherent, not both\n");

Why not just print the value of the flags?

> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	map = gntdev_alloc_map(priv, count, dmabuf_flags);
> +	if (!map)
> +		return ERR_PTR(-ENOMEM);
> +
> +	if (unlikely(gntdev_account_mapped_pages(count))) {
> +		pr_debug("can't map: over limit\n");


I think printing @count value here would be useful.


> +		gntdev_put_map(NULL, map);
> +		return ERR_PTR(-ENOMEM);
> +	}
> +	return map;
>   }
>   
>   int gntdev_dmabuf_exp_from_refs(struct gntdev_priv *priv, int flags,
>   				int count, u32 domid, u32 *refs, u32 *fd)
>   {
> +	struct gntdev_grant_map *map;
> +	struct gntdev_dmabuf_export_args args;
> +	int i, ret;
> +
>   	*fd = -1;


Is this still needed?

> -	return -EINVAL;
> +
> +	map = dmabuf_exp_alloc_backing_storage(priv, flags, count);
> +	if (IS_ERR(map))
> +		return PTR_ERR(map);
> +
> +	for (i = 0; i < count; i++) {
> +		map->grants[i].domid = domid;
> +		map->grants[i].ref = refs[i];
> +	}
> +
> +	mutex_lock(&priv->lock);
> +	gntdev_add_map(priv, map);
> +	mutex_unlock(&priv->lock);
> +
> +	map->flags |= GNTMAP_host_map;
> +#if defined(CONFIG_X86)
> +	map->flags |= GNTMAP_device_map;
> +#endif
> +
> +	ret = gntdev_map_grant_pages(map);
> +	if (ret < 0)
> +		goto out;
> +
> +	args.priv = priv;
> +	args.map = map;
> +	args.dev = priv->dma_dev;
> +	args.dmabuf_priv = priv->dmabuf_priv;
> +	args.count = map->count;
> +	args.pages = map->pages;
> +
> +	ret = dmabuf_exp_from_pages(&args);
> +	if (ret < 0)
> +		goto out;
> +
> +	*fd = args.fd;
> +	return 0;
> +
> +out:
> +	gntdev_remove_map(priv, map);
> +	return ret;
>   }
>   
>   /* DMA buffer import support. */
> @@ -63,6 +525,10 @@ struct gntdev_dmabuf_priv *gntdev_dmabuf_init(void)
>   	if (!priv)
>   		return ERR_PTR(-ENOMEM);
>   
> +	mutex_init(&priv->lock);
> +	INIT_LIST_HEAD(&priv->exp_list);
> +	INIT_LIST_HEAD(&priv->exp_wait_list);
> +
>   	return priv;
>   }
>   
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index e82660d81d7e..5f93cd534840 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -262,6 +262,16 @@ void gntdev_put_map(struct gntdev_priv *priv, struct gntdev_grant_map *map)
>   	gntdev_free_map(map);
>   }
>   
> +#ifdef CONFIG_XEN_GNTDEV_DMABUF
> +void gntdev_remove_map(struct gntdev_priv *priv, struct gntdev_grant_map *map)
> +{
> +	mutex_lock(&priv->lock);
> +	list_del(&map->next);
> +	gntdev_put_map(NULL /* already removed */, map);


Why not pass call gntdev_put_map(priv, map) and then not have this 
routine at all?

I really dislike the fact that we are taking a lock here that 
gntdev_put_map() takes as well, although not with NULL argument. (And 
yes, I see that gntdev_release() does it too.)


-boris


> +	mutex_unlock(&priv->lock);
> +}
> +#endif
> +
>   /* ------------------------------------------------------------------ */
>   
>   static int find_grant_ptes(pte_t *pte, pgtable_t token,
> 

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