[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;
> +}
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;
> > +}
@@ -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
@@ -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);
@@ -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,
@@ -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);