Re: [PATCH 6/8] xen/gntdev: Implement dma-buf export functionality
From: Oleksandr Andrushchenko
Date: Thu May 31 2018 - 01:55:45 EST
On 05/31/2018 02:10 AM, Dongwon Kim wrote:
On Fri, May 25, 2018 at 06:33:29PM +0300, Oleksandr Andrushchenko wrote:
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
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.
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
---
drivers/xen/gntdev.c | 478 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 476 insertions(+), 2 deletions(-)
diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 9e450622af1a..52abc6cd5846 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -4,6 +4,8 @@
* Device for accessing (in user-space) pages that have been granted by other
* domains.
*
+ * DMA buffer implementation is based on drivers/gpu/drm/drm_prime.c.
+ *
* Copyright (c) 2006-2007, D G Murray.
* (c) 2009 Gerd Hoffmann <kraxel@xxxxxxxxxx>
* (c) 2018 Oleksandr Andrushchenko, EPAM Systems Inc.
@@ -41,6 +43,9 @@
#ifdef CONFIG_XEN_GRANT_DMA_ALLOC
#include <linux/of_device.h>
#endif
+#ifdef CONFIG_XEN_GNTDEV_DMABUF
+#include <linux/dma-buf.h>
+#endif
#include <xen/xen.h>
#include <xen/grant_table.h>
@@ -81,6 +86,17 @@ struct gntdev_priv {
/* Device for which DMA memory is allocated. */
struct device *dma_dev;
#endif
+
+#ifdef CONFIG_XEN_GNTDEV_DMABUF
+ /* Private data of the hyper DMA buffers. */
+
+ /* List of exported DMA buffers. */
+ struct list_head dmabuf_exp_list;
+ /* List of wait objects. */
+ struct list_head dmabuf_exp_wait_list;
+ /* This is the lock which protects dma_buf_xxx lists. */
+ struct mutex dmabuf_lock;
+#endif
};
struct unmap_notify {
@@ -125,12 +141,38 @@ struct grant_map {
#ifdef CONFIG_XEN_GNTDEV_DMABUF
struct xen_dmabuf {
+ struct gntdev_priv *priv;
+ struct dma_buf *dmabuf;
+ struct list_head next;
+ int fd;
+
union {
+ struct {
+ /* Exported buffers are reference counted. */
+ struct kref refcount;
+ struct grant_map *map;
+ } exp;
struct {
/* Granted references of the imported buffer. */
grant_ref_t *refs;
} imp;
} u;
+
+ /* Number of pages this buffer has. */
+ int nr_pages;
+ /* Pages of this buffer. */
+ struct page **pages;
+};
+
+struct xen_dmabuf_wait_obj {
+ struct list_head next;
+ struct xen_dmabuf *xen_dmabuf;
+ struct completion completion;
+};
+
+struct xen_dmabuf_attachment {
+ struct sg_table *sgt;
+ enum dma_data_direction dir;
};
#endif
@@ -320,6 +362,16 @@ static void gntdev_put_map(struct gntdev_priv *priv, struct grant_map *map)
gntdev_free_map(map);
}
+#ifdef CONFIG_XEN_GNTDEV_DMABUF
+static void gntdev_remove_map(struct gntdev_priv *priv, struct grant_map *map)
+{
+ mutex_lock(&priv->lock);
+ list_del(&map->next);
+ gntdev_put_map(NULL /* already removed */, map);
+ mutex_unlock(&priv->lock);
+}
+#endif
+
/* ------------------------------------------------------------------ */
static int find_grant_ptes(pte_t *pte, pgtable_t token,
@@ -628,6 +680,12 @@ static int gntdev_open(struct inode *inode, struct file *flip)
INIT_LIST_HEAD(&priv->freeable_maps);
mutex_init(&priv->lock);
+#ifdef CONFIG_XEN_GNTDEV_DMABUF
+ mutex_init(&priv->dmabuf_lock);
+ INIT_LIST_HEAD(&priv->dmabuf_exp_list);
+ INIT_LIST_HEAD(&priv->dmabuf_exp_wait_list);
+#endif
+
if (use_ptemod) {
priv->mm = get_task_mm(current);
if (!priv->mm) {
@@ -1053,17 +1111,433 @@ static long gntdev_ioctl_grant_copy(struct gntdev_priv *priv, void __user *u)
/* DMA buffer export support. */
/* ------------------------------------------------------------------ */
+/* ------------------------------------------------------------------ */
+/* Implementation of wait for exported DMA buffer to be released. */
+/* ------------------------------------------------------------------ */
+
+static void dmabuf_exp_release(struct kref *kref);
+
+static struct xen_dmabuf_wait_obj *
+dmabuf_exp_wait_obj_new(struct gntdev_priv *priv,
+ struct xen_dmabuf *xen_dmabuf)
+{
+ struct xen_dmabuf_wait_obj *obj;
+
+ obj = kzalloc(sizeof(*obj), GFP_KERNEL);
+ if (!obj)
+ return ERR_PTR(-ENOMEM);
+
+ init_completion(&obj->completion);
+ obj->xen_dmabuf = xen_dmabuf;
+
+ mutex_lock(&priv->dmabuf_lock);
+ list_add(&obj->next, &priv->dmabuf_exp_wait_list);
+ /* Put our reference and wait for xen_dmabuf's release to fire. */
+ kref_put(&xen_dmabuf->u.exp.refcount, dmabuf_exp_release);
+ mutex_unlock(&priv->dmabuf_lock);
+ return obj;
+}
+
+static void dmabuf_exp_wait_obj_free(struct gntdev_priv *priv,
+ struct xen_dmabuf_wait_obj *obj)
+{
+ struct xen_dmabuf_wait_obj *cur_obj, *q;
+
+ mutex_lock(&priv->dmabuf_lock);
+ list_for_each_entry_safe(cur_obj, q, &priv->dmabuf_exp_wait_list, next)
+ if (cur_obj == obj) {
+ list_del(&obj->next);
+ kfree(obj);
+ break;
+ }
+ mutex_unlock(&priv->dmabuf_lock);
+}
+
+static int dmabuf_exp_wait_obj_wait(struct xen_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_priv *priv,
+ struct xen_dmabuf *xen_dmabuf)
+{
+ struct xen_dmabuf_wait_obj *obj, *q;
+
+ list_for_each_entry_safe(obj, q, &priv->dmabuf_exp_wait_list, next)
+ if (obj->xen_dmabuf == xen_dmabuf) {
+ pr_debug("Found xen_dmabuf in the wait list, wake\n");
+ complete_all(&obj->completion);
+ }
+}
+
+static struct xen_dmabuf *
+dmabuf_exp_wait_obj_get_by_fd(struct gntdev_priv *priv, int fd)
+{
+ struct xen_dmabuf *q, *xen_dmabuf, *ret = ERR_PTR(-ENOENT);
+
+ mutex_lock(&priv->dmabuf_lock);
+ list_for_each_entry_safe(xen_dmabuf, q, &priv->dmabuf_exp_list, next)
+ if (xen_dmabuf->fd == fd) {
+ pr_debug("Found xen_dmabuf in the wait list\n");
+ kref_get(&xen_dmabuf->u.exp.refcount);
+ ret = xen_dmabuf;
+ break;
+ }
+ mutex_unlock(&priv->dmabuf_lock);
+ return ret;
+}
+
static int dmabuf_exp_wait_released(struct gntdev_priv *priv, int fd,
int wait_to_ms)
{
- return -ETIMEDOUT;
+ struct xen_dmabuf *xen_dmabuf;
+ struct xen_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.
+ */
+ xen_dmabuf = dmabuf_exp_wait_obj_get_by_fd(priv, fd);
+ if (IS_ERR(xen_dmabuf))
+ return PTR_ERR(xen_dmabuf);
+
+ /*
+ * xen_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, xen_dmabuf);
+ if (IS_ERR(obj)) {
+ pr_err("Failed to setup wait object, ret %ld\n", PTR_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 xen_dmabuf_attachment *xen_dmabuf_attach;
+
+ xen_dmabuf_attach = kzalloc(sizeof(*xen_dmabuf_attach), GFP_KERNEL);
+ if (!xen_dmabuf_attach)
+ return -ENOMEM;
+
+ xen_dmabuf_attach->dir = DMA_NONE;
+ attach->priv = xen_dmabuf_attach;
+ /* Might need to pin the pages of the buffer now. */
+ return 0;
+}
+
+static void dmabuf_exp_ops_detach(struct dma_buf *dma_buf,
+ struct dma_buf_attachment *attach)
+{
+ struct xen_dmabuf_attachment *xen_dmabuf_attach = attach->priv;
+
+ if (xen_dmabuf_attach) {
+ struct sg_table *sgt = xen_dmabuf_attach->sgt;
+
+ if (sgt) {
+ if (xen_dmabuf_attach->dir != DMA_NONE)
+ dma_unmap_sg_attrs(attach->dev, sgt->sgl,
+ sgt->nents,
+ xen_dmabuf_attach->dir,
+ DMA_ATTR_SKIP_CPU_SYNC);
+ sg_free_table(sgt);
+ }
+
+ kfree(sgt);
+ kfree(xen_dmabuf_attach);
+ attach->priv = NULL;
+ }
+ /* Might need to unpin the pages of the buffer now. */
+}
+
+static struct sg_table *
+dmabuf_exp_ops_map_dma_buf(struct dma_buf_attachment *attach,
+ enum dma_data_direction dir)
+{
+ struct xen_dmabuf_attachment *xen_dmabuf_attach = attach->priv;
+ struct xen_dmabuf *xen_dmabuf = attach->dmabuf->priv;
+ struct sg_table *sgt;
+
+ pr_debug("Mapping %d pages for dev %p\n", xen_dmabuf->nr_pages,
+ attach->dev);
+
+ if (WARN_ON(dir == DMA_NONE || !xen_dmabuf_attach))
+ return ERR_PTR(-EINVAL);
+
+ /* Return the cached mapping when possible. */
+ if (xen_dmabuf_attach->dir == dir)
+ return xen_dmabuf_attach->sgt;
may need to check xen_dmabuf_attach->sgt == NULL (i.e. first time mapping)?
Also, I am not sure if this mechanism of reusing previously generated sgt
for other mappings is universally ok for any use-cases... I don't know if
it is acceptable as per the specification.
Well, I was not sure about this piece of code as well,
so I'll probably allocate a new sgt each time and do not reuse it
as now
+
+ /*
+ * Two mappings with different directions for the same attachment are
+ * not allowed.
+ */
+ if (WARN_ON(xen_dmabuf_attach->dir != DMA_NONE))
+ return ERR_PTR(-EBUSY);
+
+ sgt = dmabuf_pages_to_sgt(xen_dmabuf->pages, xen_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 {
+ xen_dmabuf_attach->sgt = sgt;
+ xen_dmabuf_attach->dir = dir;
+ }
+ }
+ if (IS_ERR(sgt))
+ pr_err("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(). */
Not sure if it's ok to do nothing here because the spec says this function is
mandatory and it should unmap and "release" &sg_table associated with it.
/**
* @unmap_dma_buf:
*
* 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.
*/
Yes, as I say at the top of the file dma-buf handling is DRM PRIME
based, so I have the workflow just like in there.
Do you think we have to be more strict and rework this?
Daniel, what do you think?
+}
+
+static void dmabuf_exp_release(struct kref *kref)
+{
+ struct xen_dmabuf *xen_dmabuf =
+ container_of(kref, struct xen_dmabuf, u.exp.refcount);
+
+ dmabuf_exp_wait_obj_signal(xen_dmabuf->priv, xen_dmabuf);
+ list_del(&xen_dmabuf->next);
+ kfree(xen_dmabuf);
+}
+
+static void dmabuf_exp_ops_release(struct dma_buf *dma_buf)
+{
+ struct xen_dmabuf *xen_dmabuf = dma_buf->priv;
+ struct gntdev_priv *priv = xen_dmabuf->priv;
+
+ gntdev_remove_map(priv, xen_dmabuf->u.exp.map);
+ mutex_lock(&priv->dmabuf_lock);
+ kref_put(&xen_dmabuf->u.exp.refcount, dmabuf_exp_release);
+ mutex_unlock(&priv->dmabuf_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,
+};
+
+static int dmabuf_export(struct gntdev_priv *priv, struct grant_map *map,
+ int *fd)
+{
+ DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+ struct xen_dmabuf *xen_dmabuf;
+ int ret = 0;
+
+ xen_dmabuf = kzalloc(sizeof(*xen_dmabuf), GFP_KERNEL);
+ if (!xen_dmabuf)
+ return -ENOMEM;
+
+ kref_init(&xen_dmabuf->u.exp.refcount);
+
+ xen_dmabuf->priv = priv;
+ xen_dmabuf->nr_pages = map->count;
+ xen_dmabuf->pages = map->pages;
+ xen_dmabuf->u.exp.map = map;
+
+ exp_info.exp_name = KBUILD_MODNAME;
+ if (map->dma_dev->driver && map->dma_dev->driver->owner)
+ exp_info.owner = map->dma_dev->driver->owner;
+ else
+ exp_info.owner = THIS_MODULE;
+ exp_info.ops = &dmabuf_exp_ops;
+ exp_info.size = map->count << PAGE_SHIFT;
+ exp_info.flags = O_RDWR;
+ exp_info.priv = xen_dmabuf;
+
+ xen_dmabuf->dmabuf = dma_buf_export(&exp_info);
+ if (IS_ERR(xen_dmabuf->dmabuf)) {
+ ret = PTR_ERR(xen_dmabuf->dmabuf);
+ xen_dmabuf->dmabuf = NULL;
+ goto fail;
+ }
+
+ ret = dma_buf_fd(xen_dmabuf->dmabuf, O_CLOEXEC);
+ if (ret < 0)
+ goto fail;
+
+ xen_dmabuf->fd = ret;
+ *fd = ret;
+
+ pr_debug("Exporting DMA buffer with fd %d\n", ret);
+
+ mutex_lock(&priv->dmabuf_lock);
+ list_add(&xen_dmabuf->next, &priv->dmabuf_exp_list);
+ mutex_unlock(&priv->dmabuf_lock);
+ return 0;
+
+fail:
+ if (xen_dmabuf->dmabuf)
+ dma_buf_put(xen_dmabuf->dmabuf);
+ kfree(xen_dmabuf);
+ return ret;
+}
+
+static struct grant_map *
+dmabuf_exp_alloc_backing_storage(struct gntdev_priv *priv, int dmabuf_flags,
+ int count)
+{
+ struct 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_err("Wrong dma-buf flags: either WC or coherent, not both\n");
+ return ERR_PTR(-EINVAL);
+ }
+
+ map = gntdev_alloc_map(priv, count, dmabuf_flags);
+ if (!map)
+ return ERR_PTR(-ENOMEM);
+
+ if (unlikely(atomic_add_return(count, &pages_mapped) > limit)) {
+ pr_err("can't map: over limit\n");
+ gntdev_put_map(NULL, map);
+ return ERR_PTR(-ENOMEM);
+ }
+ return map;
}
When and how would this allocation be freed? I don't see any ioctl for freeing up
shared pages.
on xen_dmabuf.release callback which is refcounted
static int dmabuf_exp_from_refs(struct gntdev_priv *priv, int flags,
int count, u32 domid, u32 *refs, u32 *fd)
{
+ struct grant_map *map;
+ int i, ret;
+
*fd = -1;
- return -EINVAL;
+
+ if (use_ptemod) {
+ pr_err("Cannot provide dma-buf: use_ptemode %d\n",
+ use_ptemod);
+ 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 = map_grant_pages(map);
+ if (ret < 0)
+ goto out;
+
+ ret = dmabuf_export(priv, map, fd);
+ if (ret < 0)
+ goto out;
+
+ return 0;
+
+out:
+ gntdev_remove_map(priv, map);
+ return ret;
}
/* ------------------------------------------------------------------ */
--
2.17.0