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Merge branch 'for-linus-3.4' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf

Browse Source 
Pull dma-buf updates from Sumit Semwal:
 "This includes the following key items:

   - kernel cpu access support,
   - flag-passing to dma_buf_fd,
   - relevant Documentation updates, and
   - some minor cleanups and fixes.

  These changes are needed for the drm prime/dma-buf interface code that
  Dave Airlie plans to submit in this merge window."

* 'for-linus-3.4' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf:
  dma-buf: correct dummy function declarations.
  dma-buf: document fd flags and O_CLOEXEC requirement
  dma_buf: Add documentation for the new cpu access support
  dma-buf: add support for kernel cpu access
  dma-buf: don't hold the mutex around map/unmap calls
  dma-buf: add get_dma_buf()
  dma-buf: pass flags into dma_buf_fd.
  dma-buf: add dma_data_direction to unmap dma_buf_op
  dma-buf: Move code out of mutex-protected section in dma_buf_attach()
  dma-buf: Return error instead of using a goto statement when possible
  dma-buf: Remove unneeded sanity checks
  dma-buf: Constify ops argument to dma_buf_export()
This commit is contained in:
Linus Torvalds 2012-03-28 15:02:41 -07:00
commit ed0bb8ea05
3 changed files with 345 additions and 37 deletions
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120
Documentation/dma-buf-sharing.txt
View File

@ -32,8 +32,12 @@ The buffer-user
*IMPORTANT*: [see https://lkml.org/lkml/2011/12/20/211 for more details]
For this first version, A buffer shared using the dma_buf sharing API:
- *may* be exported to user space using "mmap" *ONLY* by exporter, outside of
this framework.
- may be used *ONLY* by importers that do not need CPU access to the buffer.
this framework.
- with this new iteration of the dma-buf api cpu access from the kernel has been
enable, see below for the details.
dma-buf operations for device dma only
--------------------------------------
The dma_buf buffer sharing API usage contains the following steps:
@ -219,10 +223,120 @@ NOTES:
If the exporter chooses not to allow an attach() operation once a
map_dma_buf() API has been called, it simply returns an error.
Miscellaneous notes:
Kernel cpu access to a dma-buf buffer object
--------------------------------------------
The motivation to allow cpu access from the kernel to a dma-buf object from the
importers side are:
- fallback operations, e.g. if the devices is connected to a usb bus and the
kernel needs to shuffle the data around first before sending it away.
- full transparency for existing users on the importer side, i.e. userspace
should not notice the difference between a normal object from that subsystem
and an imported one backed by a dma-buf. This is really important for drm
opengl drivers that expect to still use all the existing upload/download
paths.
Access to a dma_buf from the kernel context involves three steps:
1. Prepare access, which invalidate any necessary caches and make the object
available for cpu access.
2. Access the object page-by-page with the dma_buf map apis
3. Finish access, which will flush any necessary cpu caches and free reserved
resources.
1. Prepare access
Before an importer can access a dma_buf object with the cpu from the kernel
context, it needs to notify the exporter of the access that is about to
happen.
Interface:
int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
size_t start, size_t len,
enum dma_data_direction direction)
This allows the exporter to ensure that the memory is actually available for
cpu access - the exporter might need to allocate or swap-in and pin the
backing storage. The exporter also needs to ensure that cpu access is
coherent for the given range and access direction. The range and access
direction can be used by the exporter to optimize the cache flushing, i.e.
access outside of the range or with a different direction (read instead of
write) might return stale or even bogus data (e.g. when the exporter needs to
copy the data to temporary storage).
This step might fail, e.g. in oom conditions.
2. Accessing the buffer
To support dma_buf objects residing in highmem cpu access is page-based using
an api similar to kmap. Accessing a dma_buf is done in aligned chunks of
PAGE_SIZE size. Before accessing a chunk it needs to be mapped, which returns
a pointer in kernel virtual address space. Afterwards the chunk needs to be
unmapped again. There is no limit on how often a given chunk can be mapped
and unmapped, i.e. the importer does not need to call begin_cpu_access again
before mapping the same chunk again.
Interfaces:
void *dma_buf_kmap(struct dma_buf *, unsigned long);
void dma_buf_kunmap(struct dma_buf *, unsigned long, void *);
There are also atomic variants of these interfaces. Like for kmap they
facilitate non-blocking fast-paths. Neither the importer nor the exporter (in
the callback) is allowed to block when using these.
Interfaces:
void *dma_buf_kmap_atomic(struct dma_buf *, unsigned long);
void dma_buf_kunmap_atomic(struct dma_buf *, unsigned long, void *);
For importers all the restrictions of using kmap apply, like the limited
supply of kmap_atomic slots. Hence an importer shall only hold onto at most 2
atomic dma_buf kmaps at the same time (in any given process context).
dma_buf kmap calls outside of the range specified in begin_cpu_access are
undefined. If the range is not PAGE_SIZE aligned, kmap needs to succeed on
the partial chunks at the beginning and end but may return stale or bogus
data outside of the range (in these partial chunks).
Note that these calls need to always succeed. The exporter needs to complete
any preparations that might fail in begin_cpu_access.
3. Finish access
When the importer is done accessing the range specified in begin_cpu_access,
it needs to announce this to the exporter (to facilitate cache flushing and
unpinning of any pinned resources). The result of of any dma_buf kmap calls
after end_cpu_access is undefined.
Interface:
void dma_buf_end_cpu_access(struct dma_buf *dma_buf,
size_t start, size_t len,
enum dma_data_direction dir);
Miscellaneous notes
-------------------
- Any exporters or users of the dma-buf buffer sharing framework must have
a 'select DMA_SHARED_BUFFER' in their respective Kconfigs.
- In order to avoid fd leaks on exec, the FD_CLOEXEC flag must be set
on the file descriptor. This is not just a resource leak, but a
potential security hole. It could give the newly exec'd application
access to buffers, via the leaked fd, to which it should otherwise
not be permitted access.
The problem with doing this via a separate fcntl() call, versus doing it
atomically when the fd is created, is that this is inherently racy in a
multi-threaded app[3]. The issue is made worse when it is library code
opening/creating the file descriptor, as the application may not even be
aware of the fd's.
To avoid this problem, userspace must have a way to request O_CLOEXEC
flag be set when the dma-buf fd is created. So any API provided by
the exporting driver to create a dmabuf fd must provide a way to let
userspace control setting of O_CLOEXEC flag passed in to dma_buf_fd().
References:
[1] struct dma_buf_ops in include/linux/dma-buf.h
[2] All interfaces mentioned above defined in include/linux/dma-buf.h
[3] https://lwn.net/Articles/236486/

165
drivers/base/dma-buf.c
View File

@ -71,7 +71,7 @@ static inline int is_dma_buf_file(struct file *file)
* ops, or error in allocating struct dma_buf, will return negative error.
*
*/
struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
struct dma_buf *dma_buf_export(void *priv, const struct dma_buf_ops *ops,
size_t size, int flags)
{
struct dma_buf *dmabuf;
@ -80,7 +80,9 @@ struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
if (WARN_ON(!priv || !ops
|| !ops->map_dma_buf
|| !ops->unmap_dma_buf
|| !ops->release)) {
|| !ops->release
|| !ops->kmap_atomic
|| !ops->kmap)) {
return ERR_PTR(-EINVAL);
}
@ -107,17 +109,18 @@ EXPORT_SYMBOL_GPL(dma_buf_export);
/**
* dma_buf_fd - returns a file descriptor for the given dma_buf
* @dmabuf: [in] pointer to dma_buf for which fd is required.
* @flags: [in] flags to give to fd
*
* On success, returns an associated 'fd'. Else, returns error.
*/
int dma_buf_fd(struct dma_buf *dmabuf)
int dma_buf_fd(struct dma_buf *dmabuf, int flags)
{
int error, fd;
if (!dmabuf || !dmabuf->file)
return -EINVAL;
error = get_unused_fd();
error = get_unused_fd_flags(flags);
if (error < 0)
return error;
fd = error;
@ -185,17 +188,18 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
struct dma_buf_attachment *attach;
int ret;
if (WARN_ON(!dmabuf || !dev || !dmabuf->ops))
if (WARN_ON(!dmabuf || !dev))
return ERR_PTR(-EINVAL);
attach = kzalloc(sizeof(struct dma_buf_attachment), GFP_KERNEL);
if (attach == NULL)
goto err_alloc;
mutex_lock(&dmabuf->lock);
return ERR_PTR(-ENOMEM);
attach->dev = dev;
attach->dmabuf = dmabuf;
mutex_lock(&dmabuf->lock);
if (dmabuf->ops->attach) {
ret = dmabuf->ops->attach(dmabuf, dev, attach);
if (ret)
@ -206,8 +210,6 @@ struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
mutex_unlock(&dmabuf->lock);
return attach;
err_alloc:
return ERR_PTR(-ENOMEM);
err_attach:
kfree(attach);
mutex_unlock(&dmabuf->lock);
@ -224,7 +226,7 @@ EXPORT_SYMBOL_GPL(dma_buf_attach);
*/
void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
{
if (WARN_ON(!dmabuf || !attach || !dmabuf->ops))
if (WARN_ON(!dmabuf || !attach))
return;
mutex_lock(&dmabuf->lock);
@ -255,13 +257,10 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
might_sleep();
if (WARN_ON(!attach || !attach->dmabuf || !attach->dmabuf->ops))
if (WARN_ON(!attach || !attach->dmabuf))
return ERR_PTR(-EINVAL);
mutex_lock(&attach->dmabuf->lock);
if (attach->dmabuf->ops->map_dma_buf)
sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
mutex_unlock(&attach->dmabuf->lock);
sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
return sg_table;
}
@ -273,19 +272,137 @@ EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
* dma_buf_ops.
* @attach: [in] attachment to unmap buffer from
* @sg_table: [in] scatterlist info of the buffer to unmap
* @direction: [in] direction of DMA transfer
*
*/
void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
struct sg_table *sg_table)
struct sg_table *sg_table,
enum dma_data_direction direction)
{
if (WARN_ON(!attach || !attach->dmabuf || !sg_table
|| !attach->dmabuf->ops))
if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
return;
mutex_lock(&attach->dmabuf->lock);
if (attach->dmabuf->ops->unmap_dma_buf)
attach->dmabuf->ops->unmap_dma_buf(attach, sg_table);
mutex_unlock(&attach->dmabuf->lock);
attach->dmabuf->ops->unmap_dma_buf(attach, sg_table,
direction);
}
EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
/**
* dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the
* cpu in the kernel context. Calls begin_cpu_access to allow exporter-specific
* preparations. Coherency is only guaranteed in the specified range for the
* specified access direction.
* @dma_buf: [in] buffer to prepare cpu access for.
* @start: [in] start of range for cpu access.
* @len: [in] length of range for cpu access.
* @direction: [in] length of range for cpu access.
*
* Can return negative error values, returns 0 on success.
*/
int dma_buf_begin_cpu_access(struct dma_buf *dmabuf, size_t start, size_t len,
enum dma_data_direction direction)
{
int ret = 0;
if (WARN_ON(!dmabuf))
return -EINVAL;
if (dmabuf->ops->begin_cpu_access)
ret = dmabuf->ops->begin_cpu_access(dmabuf, start, len, direction);
return ret;
}
EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);
/**
* dma_buf_end_cpu_access - Must be called after accessing a dma_buf from the
* cpu in the kernel context. Calls end_cpu_access to allow exporter-specific
* actions. Coherency is only guaranteed in the specified range for the
* specified access direction.
* @dma_buf: [in] buffer to complete cpu access for.
* @start: [in] start of range for cpu access.
* @len: [in] length of range for cpu access.
* @direction: [in] length of range for cpu access.
*
* This call must always succeed.
*/
void dma_buf_end_cpu_access(struct dma_buf *dmabuf, size_t start, size_t len,
enum dma_data_direction direction)
{
WARN_ON(!dmabuf);
if (dmabuf->ops->end_cpu_access)
dmabuf->ops->end_cpu_access(dmabuf, start, len, direction);
}
EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);
/**
* dma_buf_kmap_atomic - Map a page of the buffer object into kernel address
* space. The same restrictions as for kmap_atomic and friends apply.
* @dma_buf: [in] buffer to map page from.
* @page_num: [in] page in PAGE_SIZE units to map.
*
* This call must always succeed, any necessary preparations that might fail
* need to be done in begin_cpu_access.
*/
void *dma_buf_kmap_atomic(struct dma_buf *dmabuf, unsigned long page_num)
{
WARN_ON(!dmabuf);
return dmabuf->ops->kmap_atomic(dmabuf, page_num);
}
EXPORT_SYMBOL_GPL(dma_buf_kmap_atomic);
/**
* dma_buf_kunmap_atomic - Unmap a page obtained by dma_buf_kmap_atomic.
* @dma_buf: [in] buffer to unmap page from.
* @page_num: [in] page in PAGE_SIZE units to unmap.
* @vaddr: [in] kernel space pointer obtained from dma_buf_kmap_atomic.
*
* This call must always succeed.
*/
void dma_buf_kunmap_atomic(struct dma_buf *dmabuf, unsigned long page_num,
void *vaddr)
{
WARN_ON(!dmabuf);
if (dmabuf->ops->kunmap_atomic)
dmabuf->ops->kunmap_atomic(dmabuf, page_num, vaddr);
}
EXPORT_SYMBOL_GPL(dma_buf_kunmap_atomic);
/**
* dma_buf_kmap - Map a page of the buffer object into kernel address space. The
* same restrictions as for kmap and friends apply.
* @dma_buf: [in] buffer to map page from.
* @page_num: [in] page in PAGE_SIZE units to map.
*
* This call must always succeed, any necessary preparations that might fail
* need to be done in begin_cpu_access.
*/
void *dma_buf_kmap(struct dma_buf *dmabuf, unsigned long page_num)
{
WARN_ON(!dmabuf);
return dmabuf->ops->kmap(dmabuf, page_num);
}
EXPORT_SYMBOL_GPL(dma_buf_kmap);
/**
* dma_buf_kunmap - Unmap a page obtained by dma_buf_kmap.
* @dma_buf: [in] buffer to unmap page from.
* @page_num: [in] page in PAGE_SIZE units to unmap.
* @vaddr: [in] kernel space pointer obtained from dma_buf_kmap.
*
* This call must always succeed.
*/
void dma_buf_kunmap(struct dma_buf *dmabuf, unsigned long page_num,
void *vaddr)
{
WARN_ON(!dmabuf);
if (dmabuf->ops->kunmap)
dmabuf->ops->kunmap(dmabuf, page_num, vaddr);
}
EXPORT_SYMBOL_GPL(dma_buf_kunmap);

97
include/linux/dma-buf.h
View File

@ -29,6 +29,7 @@
#include <linux/scatterlist.h>
#include <linux/list.h>
#include <linux/dma-mapping.h>
#include <linux/fs.h>
struct device;
struct dma_buf;
@ -49,6 +50,17 @@ struct dma_buf_attachment;
* @unmap_dma_buf: decreases usecount of buffer, might deallocate scatter
* pages.
* @release: release this buffer; to be called after the last dma_buf_put.
* @begin_cpu_access: [optional] called before cpu access to invalidate cpu
* caches and allocate backing storage (if not yet done)
* respectively pin the objet into memory.
* @end_cpu_access: [optional] called after cpu access to flush cashes.
* @kmap_atomic: maps a page from the buffer into kernel address
* space, users may not block until the subsequent unmap call.
* This callback must not sleep.
* @kunmap_atomic: [optional] unmaps a atomically mapped page from the buffer.
* This Callback must not sleep.
* @kmap: maps a page from the buffer into kernel address space.
* @kunmap: [optional] unmaps a page from the buffer.
*/
struct dma_buf_ops {
int (*attach)(struct dma_buf *, struct device *,
@ -63,7 +75,8 @@ struct dma_buf_ops {
struct sg_table * (*map_dma_buf)(struct dma_buf_attachment *,
enum dma_data_direction);
void (*unmap_dma_buf)(struct dma_buf_attachment *,
struct sg_table *);
struct sg_table *,
enum dma_data_direction);
/* TODO: Add try_map_dma_buf version, to return immed with -EBUSY
* if the call would block.
*/
@ -71,6 +84,14 @@ struct dma_buf_ops {
/* after final dma_buf_put() */
void (*release)(struct dma_buf *);
int (*begin_cpu_access)(struct dma_buf *, size_t, size_t,
enum dma_data_direction);
void (*end_cpu_access)(struct dma_buf *, size_t, size_t,
enum dma_data_direction);
void *(*kmap_atomic)(struct dma_buf *, unsigned long);
void (*kunmap_atomic)(struct dma_buf *, unsigned long, void *);
void *(*kmap)(struct dma_buf *, unsigned long);
void (*kunmap)(struct dma_buf *, unsigned long, void *);
};
/**
@ -86,7 +107,7 @@ struct dma_buf {
struct file *file;
struct list_head attachments;
const struct dma_buf_ops *ops;
/* mutex to serialize list manipulation and other ops */
/* mutex to serialize list manipulation and attach/detach */
struct mutex lock;
void *priv;
};
@ -109,20 +130,43 @@ struct dma_buf_attachment {
void *priv;
};
/**
* get_dma_buf - convenience wrapper for get_file.
* @dmabuf: [in] pointer to dma_buf
*
* Increments the reference count on the dma-buf, needed in case of drivers
* that either need to create additional references to the dmabuf on the
* kernel side. For example, an exporter that needs to keep a dmabuf ptr
* so that subsequent exports don't create a new dmabuf.
*/
static inline void get_dma_buf(struct dma_buf *dmabuf)
{
get_file(dmabuf->file);
}
#ifdef CONFIG_DMA_SHARED_BUFFER
struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
struct device *dev);
void dma_buf_detach(struct dma_buf *dmabuf,
struct dma_buf_attachment *dmabuf_attach);
struct dma_buf *dma_buf_export(void *priv, struct dma_buf_ops *ops,
size_t size, int flags);
int dma_buf_fd(struct dma_buf *dmabuf);
struct dma_buf *dma_buf_export(void *priv, const struct dma_buf_ops *ops,
size_t size, int flags);
int dma_buf_fd(struct dma_buf *dmabuf, int flags);
struct dma_buf *dma_buf_get(int fd);
void dma_buf_put(struct dma_buf *dmabuf);
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 *);
void dma_buf_unmap_attachment(struct dma_buf_attachment *, struct sg_table *,
enum dma_data_direction);
int dma_buf_begin_cpu_access(struct dma_buf *dma_buf, size_t start, size_t len,
enum dma_data_direction dir);
void dma_buf_end_cpu_access(struct dma_buf *dma_buf, size_t start, size_t len,
enum dma_data_direction dir);
void *dma_buf_kmap_atomic(struct dma_buf *, unsigned long);
void dma_buf_kunmap_atomic(struct dma_buf *, unsigned long, void *);
void *dma_buf_kmap(struct dma_buf *, unsigned long);
void dma_buf_kunmap(struct dma_buf *, unsigned long, void *);
#else
static inline struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
@ -138,13 +182,13 @@ static inline void dma_buf_detach(struct dma_buf *dmabuf,
}
static inline struct dma_buf *dma_buf_export(void *priv,
struct dma_buf_ops *ops,
size_t size, int flags)
const struct dma_buf_ops *ops,
size_t size, int flags)
{
return ERR_PTR(-ENODEV);
}
static inline int dma_buf_fd(struct dma_buf *dmabuf)
static inline int dma_buf_fd(struct dma_buf *dmabuf, int flags)
{
return -ENODEV;
}
@ -166,11 +210,44 @@ static inline struct sg_table *dma_buf_map_attachment(
}
static inline void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
struct sg_table *sg)
struct sg_table *sg, enum dma_data_direction dir)
{
return;
}
static inline int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
size_t start, size_t len,
enum dma_data_direction dir)
{
return -ENODEV;
}
static inline void dma_buf_end_cpu_access(struct dma_buf *dmabuf,
size_t start, size_t len,
enum dma_data_direction dir)
{
}
static inline void *dma_buf_kmap_atomic(struct dma_buf *dmabuf,
unsigned long pnum)
{
return NULL;
}
static inline void dma_buf_kunmap_atomic(struct dma_buf *dmabuf,
unsigned long pnum, void *vaddr)
{
}
static inline void *dma_buf_kmap(struct dma_buf *dmabuf, unsigned long pnum)
{
return NULL;
}
static inline void dma_buf_kunmap(struct dma_buf *dmabuf,
unsigned long pnum, void *vaddr)
{
}
#endif /* CONFIG_DMA_SHARED_BUFFER */
#endif /* __DMA_BUF_H__ */