diff mbox series

[3/6] dma-mapping: add a dma_alloc_noncontiguous API

Message ID 20210301085236.947011-4-hch@lst.de
State Accepted
Commit 7d5b5738d1514e9dd8ed452660e2a4d25beb9483
Headers show
Series [1/6] dma-mapping: add a dma_mmap_pages helper | expand

Commit Message

Christoph Hellwig March 1, 2021, 8:52 a.m. UTC 
Add a new API that returns a potentiall virtually non-contigous sg_table
and a DMA address.  This API is only properly implemented for dma-iommu
and will simply return a contigious chunk as a fallback.

The intent is that drivers can use this API if either:

 - no kernel mapping or only temporary kernel mappings are required.
   That is as a better replacement for DMA_ATTR_NO_KERNEL_MAPPING
 - a kernel mapping is required for cached and DMA mapped pages, but
   the driver also needs the pages to e.g. map them to userspace.
   In that sense it is a replacement for some aspects of the recently
   removed and never fully implemented DMA_ATTR_NON_CONSISTENT

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Tested-by: Ricardo Ribalda <ribalda@chromium.org>
---
 Documentation/core-api/dma-api.rst |  78 +++++++++++++++++++++
 include/linux/dma-map-ops.h        |  19 ++++++
 include/linux/dma-mapping.h        |  32 +++++++++
 kernel/dma/mapping.c               | 106 +++++++++++++++++++++++++++++
 4 files changed, 235 insertions(+)

Comments

Robin Murphy June 29, 2023, 5:20 p.m. UTC | #1 
[Archaeology ensues...]

On 2021-03-01 08:52, Christoph Hellwig wrote:
[...]
> +static struct sg_table *alloc_single_sgt(struct device *dev, size_t size,
> +		enum dma_data_direction dir, gfp_t gfp)
> +{
> +	struct sg_table *sgt;
> +	struct page *page;
> +
> +	sgt = kmalloc(sizeof(*sgt), gfp);
> +	if (!sgt)
> +		return NULL;
> +	if (sg_alloc_table(sgt, 1, gfp))
> +		goto out_free_sgt;
> +	page = __dma_alloc_pages(dev, size, &sgt->sgl->dma_address, dir, gfp);
> +	if (!page)
> +		goto out_free_table;
> +	sg_set_page(sgt->sgl, page, PAGE_ALIGN(size), 0);
> +	sg_dma_len(sgt->sgl) = sgt->sgl->length;
> +	return sgt;
> +out_free_table:
> +	sg_free_table(sgt);
> +out_free_sgt:
> +	kfree(sgt);
> +	return NULL;
> +}
> +
> +struct sg_table *dma_alloc_noncontiguous(struct device *dev, size_t size,
> +		enum dma_data_direction dir, gfp_t gfp, unsigned long attrs)
> +{
> +	const struct dma_map_ops *ops = get_dma_ops(dev);
> +	struct sg_table *sgt;
> +
> +	if (WARN_ON_ONCE(attrs & ~DMA_ATTR_ALLOC_SINGLE_PAGES))
> +		return NULL;
> +
> +	if (ops && ops->alloc_noncontiguous)
> +		sgt = ops->alloc_noncontiguous(dev, size, dir, gfp, attrs);
> +	else
> +		sgt = alloc_single_sgt(dev, size, dir, gfp);
> +
> +	if (sgt) {
> +		sgt->nents = 1;
> +		debug_dma_map_sg(dev, sgt->sgl, sgt->orig_nents, 1, dir);

It turns out this is liable to trip up DMA_API_DEBUG_SG (potentially 
even in the alloc_single_sgt() case), since we've filled in sgt without 
paying attention to the device's segment boundary/size parameters.

Now, it would be entirely possible to make the allocators "properly" 
partition the pages into multiple segments per those constraints, but 
given that there's no actual dma_map_sg() operation involved, and AFAIR 
the intent here is really only to describe a single DMA-contiguous 
buffer as pages, rather than represent a true scatter-gather operation, 
I'm now wondering whether it makes more sense to just make dma-debug a 
bit cleverer instead. Any other opinions?

Thanks,
Robin.

> +	}
> +	return sgt;
> +}
Tomasz Figa July 5, 2023, 11:16 a.m. UTC | #2 
On Fri, Jun 30, 2023 at 2:21 AM Robin Murphy <robin.murphy@arm.com> wrote:
>
> [Archaeology ensues...]
>
> On 2021-03-01 08:52, Christoph Hellwig wrote:
> [...]
> > +static struct sg_table *alloc_single_sgt(struct device *dev, size_t size,
> > +             enum dma_data_direction dir, gfp_t gfp)
> > +{
> > +     struct sg_table *sgt;
> > +     struct page *page;
> > +
> > +     sgt = kmalloc(sizeof(*sgt), gfp);
> > +     if (!sgt)
> > +             return NULL;
> > +     if (sg_alloc_table(sgt, 1, gfp))
> > +             goto out_free_sgt;
> > +     page = __dma_alloc_pages(dev, size, &sgt->sgl->dma_address, dir, gfp);
> > +     if (!page)
> > +             goto out_free_table;
> > +     sg_set_page(sgt->sgl, page, PAGE_ALIGN(size), 0);
> > +     sg_dma_len(sgt->sgl) = sgt->sgl->length;
> > +     return sgt;
> > +out_free_table:
> > +     sg_free_table(sgt);
> > +out_free_sgt:
> > +     kfree(sgt);
> > +     return NULL;
> > +}
> > +
> > +struct sg_table *dma_alloc_noncontiguous(struct device *dev, size_t size,
> > +             enum dma_data_direction dir, gfp_t gfp, unsigned long attrs)
> > +{
> > +     const struct dma_map_ops *ops = get_dma_ops(dev);
> > +     struct sg_table *sgt;
> > +
> > +     if (WARN_ON_ONCE(attrs & ~DMA_ATTR_ALLOC_SINGLE_PAGES))
> > +             return NULL;
> > +
> > +     if (ops && ops->alloc_noncontiguous)
> > +             sgt = ops->alloc_noncontiguous(dev, size, dir, gfp, attrs);
> > +     else
> > +             sgt = alloc_single_sgt(dev, size, dir, gfp);
> > +
> > +     if (sgt) {
> > +             sgt->nents = 1;
> > +             debug_dma_map_sg(dev, sgt->sgl, sgt->orig_nents, 1, dir);
>
> It turns out this is liable to trip up DMA_API_DEBUG_SG (potentially
> even in the alloc_single_sgt() case), since we've filled in sgt without
> paying attention to the device's segment boundary/size parameters.
>
> Now, it would be entirely possible to make the allocators "properly"
> partition the pages into multiple segments per those constraints, but
> given that there's no actual dma_map_sg() operation involved, and AFAIR
> the intent here is really only to describe a single DMA-contiguous
> buffer as pages, rather than represent a true scatter-gather operation,

Yeah, the name noncontiguous comes from potentially allocating
non-contiguous physical pages, which based on a few people I talked
with, ended up being quite confusing, but I can't really think of a
better name either.

Do we know how common devices with segment boundary/size constraints
are and how likely they are to use this API?

> I'm now wondering whether it makes more sense to just make dma-debug a
> bit cleverer instead. Any other opinions?

If we could assume that drivers for those devices shouldn't use this
API, we could just fail if the segment boundary/size are set to
something other than unlimited.

Best regards,
Tomasz

>
> Thanks,
> Robin.
>
> > +     }
> > +     return sgt;
> > +}
diff mbox series

Patch

diff --git a/Documentation/core-api/dma-api.rst b/Documentation/core-api/dma-api.rst
index 157a474ae54416..00a1d4fa3f9e4e 100644
--- a/Documentation/core-api/dma-api.rst
+++ b/Documentation/core-api/dma-api.rst
@@ -594,6 +594,84 @@  dev, size, dma_handle and dir must all be the same as those passed into
 dma_alloc_noncoherent().  cpu_addr must be the virtual address returned by
 dma_alloc_noncoherent().
 
+::
+
+	struct sg_table *
+	dma_alloc_noncontiguous(struct device *dev, size_t size,
+				enum dma_data_direction dir, gfp_t gfp,
+				unsigned long attrs);
+
+This routine allocates  <size> bytes of non-coherent and possibly non-contiguous
+memory.  It returns a pointer to struct sg_table that describes the allocated
+and DMA mapped memory, or NULL if the allocation failed. The resulting memory
+can be used for struct page mapped into a scatterlist are suitable for.
+
+The return sg_table is guaranteed to have 1 single DMA mapped segment as
+indicated by sgt->nents, but it might have multiple CPU side segments as
+indicated by sgt->orig_nents.
+
+The dir parameter specified if data is read and/or written by the device,
+see dma_map_single() for details.
+
+The gfp parameter allows the caller to specify the ``GFP_`` flags (see
+kmalloc()) for the allocation, but rejects flags used to specify a memory
+zone such as GFP_DMA or GFP_HIGHMEM.
+
+The attrs argument must be either 0 or DMA_ATTR_ALLOC_SINGLE_PAGES.
+
+Before giving the memory to the device, dma_sync_sgtable_for_device() needs
+to be called, and before reading memory written by the device,
+dma_sync_sgtable_for_cpu(), just like for streaming DMA mappings that are
+reused.
+
+::
+
+	void
+	dma_free_noncontiguous(struct device *dev, size_t size,
+			       struct sg_table *sgt,
+			       enum dma_data_direction dir)
+
+Free memory previously allocated using dma_alloc_noncontiguous().  dev, size,
+and dir must all be the same as those passed into dma_alloc_noncontiguous().
+sgt must be the pointer returned by dma_alloc_noncontiguous().
+
+::
+
+	void *
+	dma_vmap_noncontiguous(struct device *dev, size_t size,
+		struct sg_table *sgt)
+
+Return a contiguous kernel mapping for an allocation returned from
+dma_alloc_noncontiguous().  dev and size must be the same as those passed into
+dma_alloc_noncontiguous().  sgt must be the pointer returned by
+dma_alloc_noncontiguous().
+
+Once a non-contiguous allocation is mapped using this function, the
+flush_kernel_vmap_range() and invalidate_kernel_vmap_range() APIs must be used
+to manage the coherency between the kernel mapping, the device and user space
+mappings (if any).
+
+::
+
+	void
+	dma_vunmap_noncontiguous(struct device *dev, void *vaddr)
+
+Unmap a kernel mapping returned by dma_vmap_noncontiguous().  dev must be the
+same the one passed into dma_alloc_noncontiguous().  vaddr must be the pointer
+returned by dma_vmap_noncontiguous().
+
+
+::
+
+	int
+	dma_mmap_noncontiguous(struct device *dev, struct vm_area_struct *vma,
+			       size_t size, struct sg_table *sgt)
+
+Map an allocation returned from dma_alloc_noncontiguous() into a user address
+space.  dev and size must be the same as those passed into
+dma_alloc_noncontiguous().  sgt must be the pointer returned by
+dma_alloc_noncontiguous().
+
 ::
 
 	int
diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index 51872e736e7b1d..0d53a96a3d641f 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -22,6 +22,11 @@  struct dma_map_ops {
 			gfp_t gfp);
 	void (*free_pages)(struct device *dev, size_t size, struct page *vaddr,
 			dma_addr_t dma_handle, enum dma_data_direction dir);
+	struct sg_table *(*alloc_noncontiguous)(struct device *dev, size_t size,
+			enum dma_data_direction dir, gfp_t gfp,
+			unsigned long attrs);
+	void (*free_noncontiguous)(struct device *dev, size_t size,
+			struct sg_table *sgt, enum dma_data_direction dir);
 	int (*mmap)(struct device *, struct vm_area_struct *,
 			void *, dma_addr_t, size_t, unsigned long attrs);
 
@@ -198,6 +203,20 @@  static inline int dma_mmap_from_global_coherent(struct vm_area_struct *vma,
 }
 #endif /* CONFIG_DMA_DECLARE_COHERENT */
 
+/*
+ * This is the actual return value from the ->alloc_noncontiguous method.
+ * The users of the DMA API should only care about the sg_table, but to make
+ * the DMA-API internal vmaping and freeing easier we stash away the page
+ * array as well (except for the fallback case).  This can go away any time,
+ * e.g. when a vmap-variant that takes a scatterlist comes along.
+ */
+struct dma_sgt_handle {
+	struct sg_table sgt;
+	struct page **pages;
+};
+#define sgt_handle(sgt) \
+	container_of((sgt), struct dma_sgt_handle, sgt)
+
 int dma_common_get_sgtable(struct device *dev, struct sg_table *sgt,
 		void *cpu_addr, dma_addr_t dma_addr, size_t size,
 		unsigned long attrs);
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 2b8dce756e1fa1..954847f9a3e0fa 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -144,6 +144,15 @@  u64 dma_get_required_mask(struct device *dev);
 size_t dma_max_mapping_size(struct device *dev);
 bool dma_need_sync(struct device *dev, dma_addr_t dma_addr);
 unsigned long dma_get_merge_boundary(struct device *dev);
+struct sg_table *dma_alloc_noncontiguous(struct device *dev, size_t size,
+		enum dma_data_direction dir, gfp_t gfp, unsigned long attrs);
+void dma_free_noncontiguous(struct device *dev, size_t size,
+		struct sg_table *sgt, enum dma_data_direction dir);
+void *dma_vmap_noncontiguous(struct device *dev, size_t size,
+		struct sg_table *sgt);
+void dma_vunmap_noncontiguous(struct device *dev, void *vaddr);
+int dma_mmap_noncontiguous(struct device *dev, struct vm_area_struct *vma,
+		size_t size, struct sg_table *sgt);
 #else /* CONFIG_HAS_DMA */
 static inline dma_addr_t dma_map_page_attrs(struct device *dev,
 		struct page *page, size_t offset, size_t size,
@@ -257,6 +266,29 @@  static inline unsigned long dma_get_merge_boundary(struct device *dev)
 {
 	return 0;
 }
+static inline struct sg_table *dma_alloc_noncontiguous(struct device *dev,
+		size_t size, enum dma_data_direction dir, gfp_t gfp,
+		unsigned long attrs)
+{
+	return NULL;
+}
+static inline void dma_free_noncontiguous(struct device *dev, size_t size,
+		struct sg_table *sgt, enum dma_data_direction dir)
+{
+}
+static inline void *dma_vmap_noncontiguous(struct device *dev, size_t size,
+		struct sg_table *sgt)
+{
+	return NULL;
+}
+static inline void dma_vunmap_noncontiguous(struct device *dev, void *vaddr)
+{
+}
+static inline int dma_mmap_noncontiguous(struct device *dev,
+		struct vm_area_struct *vma, size_t size, struct sg_table *sgt)
+{
+	return -EINVAL;
+}
 #endif /* CONFIG_HAS_DMA */
 
 struct page *dma_alloc_pages(struct device *dev, size_t size,
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index 07f964ebcda15e..2b06a809d0b9df 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -539,6 +539,112 @@  int dma_mmap_pages(struct device *dev, struct vm_area_struct *vma,
 }
 EXPORT_SYMBOL_GPL(dma_mmap_pages);
 
+static struct sg_table *alloc_single_sgt(struct device *dev, size_t size,
+		enum dma_data_direction dir, gfp_t gfp)
+{
+	struct sg_table *sgt;
+	struct page *page;
+
+	sgt = kmalloc(sizeof(*sgt), gfp);
+	if (!sgt)
+		return NULL;
+	if (sg_alloc_table(sgt, 1, gfp))
+		goto out_free_sgt;
+	page = __dma_alloc_pages(dev, size, &sgt->sgl->dma_address, dir, gfp);
+	if (!page)
+		goto out_free_table;
+	sg_set_page(sgt->sgl, page, PAGE_ALIGN(size), 0);
+	sg_dma_len(sgt->sgl) = sgt->sgl->length;
+	return sgt;
+out_free_table:
+	sg_free_table(sgt);
+out_free_sgt:
+	kfree(sgt);
+	return NULL;
+}
+
+struct sg_table *dma_alloc_noncontiguous(struct device *dev, size_t size,
+		enum dma_data_direction dir, gfp_t gfp, unsigned long attrs)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+	struct sg_table *sgt;
+
+	if (WARN_ON_ONCE(attrs & ~DMA_ATTR_ALLOC_SINGLE_PAGES))
+		return NULL;
+
+	if (ops && ops->alloc_noncontiguous)
+		sgt = ops->alloc_noncontiguous(dev, size, dir, gfp, attrs);
+	else
+		sgt = alloc_single_sgt(dev, size, dir, gfp);
+
+	if (sgt) {
+		sgt->nents = 1;
+		debug_dma_map_sg(dev, sgt->sgl, sgt->orig_nents, 1, dir);
+	}
+	return sgt;
+}
+EXPORT_SYMBOL_GPL(dma_alloc_noncontiguous);
+
+static void free_single_sgt(struct device *dev, size_t size,
+		struct sg_table *sgt, enum dma_data_direction dir)
+{
+	__dma_free_pages(dev, size, sg_page(sgt->sgl), sgt->sgl->dma_address,
+			 dir);
+	sg_free_table(sgt);
+	kfree(sgt);
+}
+
+void dma_free_noncontiguous(struct device *dev, size_t size,
+		struct sg_table *sgt, enum dma_data_direction dir)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	debug_dma_unmap_sg(dev, sgt->sgl, sgt->orig_nents, dir);
+	if (ops && ops->free_noncontiguous)
+		ops->free_noncontiguous(dev, size, sgt, dir);
+	else
+		free_single_sgt(dev, size, sgt, dir);
+}
+EXPORT_SYMBOL_GPL(dma_free_noncontiguous);
+
+void *dma_vmap_noncontiguous(struct device *dev, size_t size,
+		struct sg_table *sgt)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+
+	if (ops && ops->alloc_noncontiguous)
+		return vmap(sgt_handle(sgt)->pages, count, VM_MAP, PAGE_KERNEL);
+	return page_address(sg_page(sgt->sgl));
+}
+EXPORT_SYMBOL_GPL(dma_vmap_noncontiguous);
+
+void dma_vunmap_noncontiguous(struct device *dev, void *vaddr)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	if (ops && ops->alloc_noncontiguous)
+		vunmap(vaddr);
+}
+EXPORT_SYMBOL_GPL(dma_vunmap_noncontiguous);
+
+int dma_mmap_noncontiguous(struct device *dev, struct vm_area_struct *vma,
+		size_t size, struct sg_table *sgt)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+
+	if (ops && ops->alloc_noncontiguous) {
+		unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+
+		if (vma->vm_pgoff >= count ||
+		    vma_pages(vma) > count - vma->vm_pgoff)
+			return -ENXIO;
+		return vm_map_pages(vma, sgt_handle(sgt)->pages, count);
+	}
+	return dma_mmap_pages(dev, vma, size, sg_page(sgt->sgl));
+}
+EXPORT_SYMBOL_GPL(dma_mmap_noncontiguous);
+
 int dma_supported(struct device *dev, u64 mask)
 {
 	const struct dma_map_ops *ops = get_dma_ops(dev);