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Subject[PATCH v3 8/9] xen/gntdev: Implement dma-buf export functionality
Date
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.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@epam.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);
+}
+
+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)
+{
+ 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;
+
+ 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");
+ 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");
+ 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;
- 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);
+ mutex_unlock(&priv->lock);
+}
+#endif
+
/* ------------------------------------------------------------------ */

static int find_grant_ptes(pte_t *pte, pgtable_t token,
--
2.17.1
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