| Message ID | 20210128145837.2250561-3-hch@lst.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/6] dma-mapping: remove the {alloc,free}_noncoherent methods | expand |
From: Christoph Hellwig > Sent: 28 January 2021 14:59 > > Add a helper to map memory allocated using dma_alloc_pages into > a user address space, similar to the dma_alloc_attrs function for > coherent allocations. > ... > +:: > + > + int > + dma_mmap_pages(struct device *dev, struct vm_area_struct *vma, > + size_t size, struct page *page) > + > +Map an allocation returned from dma_alloc_pages() into a user address space. > +dev and size must be the same as those passed into dma_alloc_pages(). > +page must be the pointer returned by dma_alloc_pages(). To be useful this needs to specify the offset into the user address area. (ie the offset in the mmap() buffer.) For example we have an fpga based PCIe card that converts internal addresses that refer to one of 512 16k 'pages' to 64bit PCIe bus master addresses. So it (sort of) contains its own iommu. So we can allocate (aligned) 16k kernel memory buffers with dma_alloc_coherent() and make them appear contiguous to the on-board PCIe bus master users. We then mmap() them into contiguous user addresses. So both 'ends' see contiguous addresses without requiring contiguous physical memory or requiring all the memory be allocated at the same time. Clearly in-kernel users have to allow for the 16k boundaries. But the large structures are accesses from user space. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst index e6d23f117308df..157a474ae54416 100644 --- a/Documentation/core-api/dma-api.rst +++ b/Documentation/core-api/dma-api.rst @@ -563,6 +563,16 @@ Free a region of memory previously allocated using dma_alloc_pages(). dev, size, dma_handle and dir must all be the same as those passed into dma_alloc_pages(). page must be the pointer returned by dma_alloc_pages(). +:: + + int + dma_mmap_pages(struct device *dev, struct vm_area_struct *vma, + size_t size, struct page *page) + +Map an allocation returned from dma_alloc_pages() into a user address space. +dev and size must be the same as those passed into dma_alloc_pages(). +page must be the pointer returned by dma_alloc_pages(). + :: void * diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index fbfa3f5abd9498..4977a748cb9483 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -263,6 +263,8 @@ struct page *dma_alloc_pages(struct device *dev, size_t size, dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp); void dma_free_pages(struct device *dev, size_t size, struct page *page, dma_addr_t dma_handle, enum dma_data_direction dir); +int dma_mmap_pages(struct device *dev, struct vm_area_struct *vma, + size_t size, struct page *page); static inline void *dma_alloc_noncoherent(struct device *dev, size_t size, dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp) diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c index 68992e35c8c3a7..c1e515496c067b 100644 --- a/kernel/dma/mapping.c +++ b/kernel/dma/mapping.c @@ -515,6 +515,19 @@ void dma_free_pages(struct device *dev, size_t size, struct page *page, } EXPORT_SYMBOL_GPL(dma_free_pages); +int dma_mmap_pages(struct device *dev, struct vm_area_struct *vma, + size_t size, struct page *page) +{ + unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT; + + if (vma->vm_pgoff >= count || vma_pages(vma) > count - vma->vm_pgoff) + return -ENXIO; + return remap_pfn_range(vma, vma->vm_start, + page_to_pfn(page) + vma->vm_pgoff, + vma_pages(vma) << PAGE_SHIFT, vma->vm_page_prot); +} +EXPORT_SYMBOL_GPL(dma_mmap_pages); + int dma_supported(struct device *dev, u64 mask) { const struct dma_map_ops *ops = get_dma_ops(dev);
Add a helper to map memory allocated using dma_alloc_pages into a user address space, similar to the dma_alloc_attrs function for coherent allocations. Signed-off-by: Christoph Hellwig <hch@lst.de> --- Documentation/core-api/dma-api.rst | 10 ++++++++++ include/linux/dma-mapping.h | 2 ++ kernel/dma/mapping.c | 13 +++++++++++++ 3 files changed, 25 insertions(+)