dma-buf updates for 3.5
-----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iQEcBAABAgAGBQJPvzQCAAoJEFErWKtxJpJdpNEIAI1sKDywvfuJK0Ik76ICj1Yt P//4/ZvROmT8w9u/Jw3BAG7K3u7NLtfht6RcrUFqMULjMUUQ/aymlY9uTbwFZ+so WCsVh5tHCULa1oUnAUv8fGMgvGoufD4ZqI/9qbuYLmBtUwPAatul51cEmQyWVvLa lJN8PzJ7whfYqNoXpR4SCp8eHY4iJ3DZFDhypdQfZbTgOTrzsoVIJnTdHUXsiRQQ E3gB2dRvyihzOD/UFac47af5wVUwtvo1N6NdQ5tJxOX9ZhVGdHaxAqF5FTlWpm6F uK100uqFHPbm/TZGtSrGD1ai8L7Hbl//LuzaODjLH9usCiYe6KzSSwf8Alg59Ws= =hsWu -----END PGP SIGNATURE----- Merge tag 'tag-for-linus-3.5' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf Pull dma-buf updates from Sumit Semwal: "Here's the first signed-tag pull request for dma-buf framework. It includes the following key items: - mmap support - vmap support - related documentation updates These are needed by various drivers to allow mmap/vmap of dma-buf shared buffers. Dave Airlie has some prime patches dependent on the vmap pull as well." * tag 'tag-for-linus-3.5' of git://git.linaro.org/people/sumitsemwal/linux-dma-buf: dma-buf: add initial vmap documentation dma-buf: minor documentation fixes. dma-buf: add vmap interface dma-buf: mmap support
This commit is contained in:
Linus Torvalds
commit
da89fb165e
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@ -29,13 +29,6 @@ The buffer-user
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in memory, mapped into its own address space, so it can access the same area
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of memory.
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*IMPORTANT*: [see https://lkml.org/lkml/2011/12/20/211 for more details]
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For this first version, A buffer shared using the dma_buf sharing API:
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- *may* be exported to user space using "mmap" *ONLY* by exporter, outside of
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this framework.
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- with this new iteration of the dma-buf api cpu access from the kernel has been
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enable, see below for the details.
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dma-buf operations for device dma only
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--------------------------------------
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@ -300,6 +293,17 @@ Access to a dma_buf from the kernel context involves three steps:
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Note that these calls need to always succeed. The exporter needs to complete
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any preparations that might fail in begin_cpu_access.
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For some cases the overhead of kmap can be too high, a vmap interface
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is introduced. This interface should be used very carefully, as vmalloc
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space is a limited resources on many architectures.
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Interfaces:
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void *dma_buf_vmap(struct dma_buf *dmabuf)
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void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
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The vmap call can fail if there is no vmap support in the exporter, or if it
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runs out of vmalloc space. Fallback to kmap should be implemented.
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3. Finish access
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When the importer is done accessing the range specified in begin_cpu_access,
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@ -313,6 +317,83 @@ Access to a dma_buf from the kernel context involves three steps:
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enum dma_data_direction dir);
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Direct Userspace Access/mmap Support
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------------------------------------
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Being able to mmap an export dma-buf buffer object has 2 main use-cases:
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- CPU fallback processing in a pipeline and
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- supporting existing mmap interfaces in importers.
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1. CPU fallback processing in a pipeline
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In many processing pipelines it is sometimes required that the cpu can access
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the data in a dma-buf (e.g. for thumbnail creation, snapshots, ...). To avoid
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the need to handle this specially in userspace frameworks for buffer sharing
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it's ideal if the dma_buf fd itself can be used to access the backing storage
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from userspace using mmap.
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Furthermore Android's ION framework already supports this (and is otherwise
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rather similar to dma-buf from a userspace consumer side with using fds as
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handles, too). So it's beneficial to support this in a similar fashion on
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dma-buf to have a good transition path for existing Android userspace.
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No special interfaces, userspace simply calls mmap on the dma-buf fd.
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2. Supporting existing mmap interfaces in exporters
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Similar to the motivation for kernel cpu access it is again important that
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the userspace code of a given importing subsystem can use the same interfaces
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with a imported dma-buf buffer object as with a native buffer object. This is
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especially important for drm where the userspace part of contemporary OpenGL,
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X, and other drivers is huge, and reworking them to use a different way to
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mmap a buffer rather invasive.
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The assumption in the current dma-buf interfaces is that redirecting the
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initial mmap is all that's needed. A survey of some of the existing
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subsystems shows that no driver seems to do any nefarious thing like syncing
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up with outstanding asynchronous processing on the device or allocating
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special resources at fault time. So hopefully this is good enough, since
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adding interfaces to intercept pagefaults and allow pte shootdowns would
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increase the complexity quite a bit.
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Interface:
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int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *,
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unsigned long);
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If the importing subsystem simply provides a special-purpose mmap call to set
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up a mapping in userspace, calling do_mmap with dma_buf->file will equally
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achieve that for a dma-buf object.
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3. Implementation notes for exporters
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Because dma-buf buffers have invariant size over their lifetime, the dma-buf
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core checks whether a vma is too large and rejects such mappings. The
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exporter hence does not need to duplicate this check.
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Because existing importing subsystems might presume coherent mappings for
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userspace, the exporter needs to set up a coherent mapping. If that's not
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possible, it needs to fake coherency by manually shooting down ptes when
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leaving the cpu domain and flushing caches at fault time. Note that all the
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dma_buf files share the same anon inode, hence the exporter needs to replace
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the dma_buf file stored in vma->vm_file with it's own if pte shootdown is
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requred. This is because the kernel uses the underlying inode's address_space
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for vma tracking (and hence pte tracking at shootdown time with
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unmap_mapping_range).
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If the above shootdown dance turns out to be too expensive in certain
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scenarios, we can extend dma-buf with a more explicit cache tracking scheme
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for userspace mappings. But the current assumption is that using mmap is
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always a slower path, so some inefficiencies should be acceptable.
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Exporters that shoot down mappings (for any reasons) shall not do any
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synchronization at fault time with outstanding device operations.
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Synchronization is an orthogonal issue to sharing the backing storage of a
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buffer and hence should not be handled by dma-buf itself. This is explictly
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mentioned here because many people seem to want something like this, but if
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different exporters handle this differently, buffer sharing can fail in
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interesting ways depending upong the exporter (if userspace starts depending
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upon this implicit synchronization).
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Miscellaneous notes
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-------------------
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@ -336,6 +417,20 @@ Miscellaneous notes
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the exporting driver to create a dmabuf fd must provide a way to let
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userspace control setting of O_CLOEXEC flag passed in to dma_buf_fd().
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- If an exporter needs to manually flush caches and hence needs to fake
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coherency for mmap support, it needs to be able to zap all the ptes pointing
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at the backing storage. Now linux mm needs a struct address_space associated
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with the struct file stored in vma->vm_file to do that with the function
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unmap_mapping_range. But the dma_buf framework only backs every dma_buf fd
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with the anon_file struct file, i.e. all dma_bufs share the same file.
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Hence exporters need to setup their own file (and address_space) association
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by setting vma->vm_file and adjusting vma->vm_pgoff in the dma_buf mmap
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callback. In the specific case of a gem driver the exporter could use the
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shmem file already provided by gem (and set vm_pgoff = 0). Exporters can then
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zap ptes by unmapping the corresponding range of the struct address_space
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associated with their own file.
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References:
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[1] struct dma_buf_ops in include/linux/dma-buf.h
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[2] All interfaces mentioned above defined in include/linux/dma-buf.h
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@ -44,8 +44,26 @@ static int dma_buf_release(struct inode *inode, struct file *file)
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return 0;
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}
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static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
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{
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struct dma_buf *dmabuf;
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if (!is_dma_buf_file(file))
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return -EINVAL;
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dmabuf = file->private_data;
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/* check for overflowing the buffer's size */
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if (vma->vm_pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) >
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dmabuf->size >> PAGE_SHIFT)
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return -EINVAL;
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return dmabuf->ops->mmap(dmabuf, vma);
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}
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static const struct file_operations dma_buf_fops = {
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.release = dma_buf_release,
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.mmap = dma_buf_mmap_internal,
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};
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/*
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@ -82,7 +100,8 @@ struct dma_buf *dma_buf_export(void *priv, const struct dma_buf_ops *ops,
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|| !ops->unmap_dma_buf
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|| !ops->release
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|| !ops->kmap_atomic
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|| !ops->kmap)) {
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|| !ops->kmap
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|| !ops->mmap)) {
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return ERR_PTR(-EINVAL);
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}
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@ -406,3 +425,81 @@ void dma_buf_kunmap(struct dma_buf *dmabuf, unsigned long page_num,
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dmabuf->ops->kunmap(dmabuf, page_num, vaddr);
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}
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EXPORT_SYMBOL_GPL(dma_buf_kunmap);
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/**
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* dma_buf_mmap - Setup up a userspace mmap with the given vma
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* @dmabuf: [in] buffer that should back the vma
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* @vma: [in] vma for the mmap
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* @pgoff: [in] offset in pages where this mmap should start within the
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* dma-buf buffer.
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*
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* This function adjusts the passed in vma so that it points at the file of the
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* dma_buf operation. It alsog adjusts the starting pgoff and does bounds
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* checking on the size of the vma. Then it calls the exporters mmap function to
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* set up the mapping.
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*
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* Can return negative error values, returns 0 on success.
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*/
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int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
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unsigned long pgoff)
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{
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if (WARN_ON(!dmabuf || !vma))
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return -EINVAL;
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/* check for offset overflow */
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if (pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) < pgoff)
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return -EOVERFLOW;
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/* check for overflowing the buffer's size */
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if (pgoff + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) >
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dmabuf->size >> PAGE_SHIFT)
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return -EINVAL;
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/* readjust the vma */
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if (vma->vm_file)
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fput(vma->vm_file);
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vma->vm_file = dmabuf->file;
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get_file(vma->vm_file);
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vma->vm_pgoff = pgoff;
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return dmabuf->ops->mmap(dmabuf, vma);
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}
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EXPORT_SYMBOL_GPL(dma_buf_mmap);
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/**
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* dma_buf_vmap - Create virtual mapping for the buffer object into kernel
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* address space. Same restrictions as for vmap and friends apply.
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* @dmabuf: [in] buffer to vmap
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*
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* This call may fail due to lack of virtual mapping address space.
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* These calls are optional in drivers. The intended use for them
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* is for mapping objects linear in kernel space for high use objects.
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* Please attempt to use kmap/kunmap before thinking about these interfaces.
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*/
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void *dma_buf_vmap(struct dma_buf *dmabuf)
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{
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if (WARN_ON(!dmabuf))
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return NULL;
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if (dmabuf->ops->vmap)
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return dmabuf->ops->vmap(dmabuf);
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return NULL;
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}
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EXPORT_SYMBOL_GPL(dma_buf_vmap);
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/**
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* dma_buf_vunmap - Unmap a vmap obtained by dma_buf_vmap.
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* @dmabuf: [in] buffer to vunmap
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*/
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void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
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{
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if (WARN_ON(!dmabuf))
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return;
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if (dmabuf->ops->vunmap)
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dmabuf->ops->vunmap(dmabuf, vaddr);
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}
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EXPORT_SYMBOL_GPL(dma_buf_vunmap);
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@ -61,6 +61,13 @@ struct dma_buf_attachment;
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* This Callback must not sleep.
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* @kmap: maps a page from the buffer into kernel address space.
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* @kunmap: [optional] unmaps a page from the buffer.
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* @mmap: used to expose the backing storage to userspace. Note that the
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* mapping needs to be coherent - if the exporter doesn't directly
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* support this, it needs to fake coherency by shooting down any ptes
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* when transitioning away from the cpu domain.
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* @vmap: [optional] creates a virtual mapping for the buffer into kernel
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* address space. Same restrictions as for vmap and friends apply.
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* @vunmap: [optional] unmaps a vmap from the buffer
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*/
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struct dma_buf_ops {
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int (*attach)(struct dma_buf *, struct device *,
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@ -92,6 +99,11 @@ struct dma_buf_ops {
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void (*kunmap_atomic)(struct dma_buf *, unsigned long, void *);
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void *(*kmap)(struct dma_buf *, unsigned long);
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void (*kunmap)(struct dma_buf *, unsigned long, void *);
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int (*mmap)(struct dma_buf *, struct vm_area_struct *vma);
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void *(*vmap)(struct dma_buf *);
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void (*vunmap)(struct dma_buf *, void *vaddr);
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};
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/**
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@ -167,6 +179,11 @@ void *dma_buf_kmap_atomic(struct dma_buf *, unsigned long);
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void dma_buf_kunmap_atomic(struct dma_buf *, unsigned long, void *);
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void *dma_buf_kmap(struct dma_buf *, unsigned long);
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void dma_buf_kunmap(struct dma_buf *, unsigned long, void *);
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int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *,
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unsigned long);
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void *dma_buf_vmap(struct dma_buf *);
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void dma_buf_vunmap(struct dma_buf *, void *vaddr);
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#else
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static inline struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
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@ -248,6 +265,22 @@ static inline void dma_buf_kunmap(struct dma_buf *dmabuf,
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unsigned long pnum, void *vaddr)
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{
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}
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static inline int dma_buf_mmap(struct dma_buf *dmabuf,
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struct vm_area_struct *vma,
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unsigned long pgoff)
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{
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return -ENODEV;
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}
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static inline void *dma_buf_vmap(struct dma_buf *dmabuf)
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{
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return NULL;
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}
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static inline void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
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{
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}
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#endif /* CONFIG_DMA_SHARED_BUFFER */
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#endif /* __DMA_BUF_H__ */
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